Design of Hot Oil System

1. TABLE OF CONTENTS

1. TABLE OF CONTENTS 1

2. PURPOSE 2

3. GENERAL 2

4. DEFINITIONS 3

5. SELECT HOT OIL 3

5.1 Hot Oil Supply Temperature 3

5.2 Heat Transfer Fluids 4

5.3 Finalize HOST 6

6. PROCESS DESIGN 7

6.1 Process Design of Hot Oil Users 7

6.2 Model the Hot Oil 7

6.3 Compile Process User Loads 7

6.4 Bypass Loop 7

6.5 Tempered Hot Oil Systems 8

6.6 Prepare a Heater Summary 8

6.7 Purge Stream and Makeup 10

7. PFD and MSD 10

8. HYDRAULICS 11

8.1 Assume All Users Are Supplied From a Common Node 11

8.2 Assume Users are Sequential 12

8.3 Either Method 13

8.4 Single Process Unit Hot Oil System 14

9. P&IDS 14

9.1 Specific Details 15

9.2 Supply of Hot Oil to Users 15

9.3 Bypass Control 16

10. PROJECT SPECIFICATIONS 16

10.1 Surge Drum 16

10.2 Hot Oil Storage Tank 18

10.3 Hot Oil Circulation Pumps 19

10.4 Additional Pumps 20

10.5 Fired Heater 21

10.6 Heat Exchangers 21

10.7 Pressure Relief Valves 23

10.8 Chemicals 25

10.9 Sidestream Filter 26

10.10 Piping and Strainers 26

10.11 Miscellaneous 27

11. FUEL SYSTEM 27

11.1 Waste Gases 28

11.2 Waste Liquids 28

11.3 Vent Gases 29

APPENDIX 1 LAB Complex Supplemental Design Information 30

2. PURPOSE

This Procedure describes the Inflection Point Engineering practice for designing hot oil systems for use in supplying heat to Inflection Point Engineering Process Units. This Procedure covers the full scope of the design, from process engineering to creating the specifications required for the Schedule A.

3. GENERAL

Hot oil systems are used to supply high temperature heat to various process users. The use of hot oil as a heating medium is called for in applications where other heat sources, mainly steam or fired heaters, are not suitable.

Steam can be used to supply heat to a process stream. Use of saturated steam is typically the first choice when the required process temperature is at least 50ºF less than the condensation temperature of high pressure steam (600 psig steam condenses at 489ºF). If hotter process temperatures are required, then saturated high pressure steam is no longer suitable. Superheated steam could be used, but only its sensible heat would be transferred and so large amounts of steam would be needed and this option becomes expensive. Very high pressure saturated steam could be used to get a higher condensation temperature but such a system would also be very expensive. A fired heater could also be used to supply heat at hotter temperatures. However, if there are multiple small process users, especially in different units, the cost of the individual heaters and the required fuel firing system becomes very expensive. Numerous fired heaters also take up a large amount of plot space.

Therefore, where there are multiple users of high temperature heat, a hot oil system can be a good choice. A single, large common hot oil heater is installed permitting one set of combustion controls and usually a heat recovery system. The “hot” hot oil is pumped to users throughout the complex. The “cold” hot oil is returned to the hot oil heater.

Hot oil systems have been used to supply heat to a large variety of Inflection Point Engineering process units. These include:

• LAB complex Units
• Phenol complex Units
• Aromatics complex Units
• Alkylation complex Units
• Naphtha complex Units
• Solvent Deasphalting Units

See for additional information related to the design of Hot Oil Systems for LAB complexes.

The need for a hot oil system needs to be determined on a case by case basis.

A typical hot oil system will consist of the following equipment: Surge Drum, Hot Oil Circulation Pumps, Fired Heater, supply and return piping, and miscellaneous supporting facilities. Since complexes that have a hot oil system often produce waste fuels that can not be disposed of otherwise, the hot oil system will often include facilities to allow the incineration of those waste fuels in the hot oil heater.

4. DEFINITIONS

4.1 Hot Oil Supply Temperature (HOST) – The temperature at which hot oil is supplied to the users.

4.2 Heater Outlet Temperature (HOT) – The temperature at the outlet of the hot oil heater. This is typically 5ºF above the HOST and accounts for heat loss throughout the system.

4.3 Normal Heater Inlet Temperature (NHIT) – The temperature at the inlet of the hot oil heater at normal heater duty

4.4 Design Heater Inlet Temperature (DHIT) – The temperature at the inlet of the hot oil heater at the design heater duty. The DHIT will be lower than the NHIT.

4.5 Process Hot Oil Flow (PHOF) – The total flow rate through all the process users.

4.6 Process Duty (PD) – The total duty of all the process users.

4.7 Maximum Bulk Temperature (MBT) – The maximum allowable temperature of hot oil leaving the hot oil heater that will allow acceptable hot oil life.

5. SELECT HOT OIL

The first steps in designing the hot oil system are determining the required Hot Oil Supply Temperature (HOST) and then selecting the appropriate hot oil. These two are interdependent. The minimum required HOST will force the selection of a particular hot oil. Once the hot oil is selected, the HOST may be reset based on the thermal properties of the hot oil.

5.1 Hot Oil Supply Temperature

Base the hot oil supply temperature on supplying the highest temperature process exchanger service with a reasonable amount of flow and approach temperature. As a general rule, we want the hot oil temperature leaving a reboiler to be at least 50F above the process side outlet temperature; the difference can be 25ºF for other services. For example, if we have a reboiler service going from 473F inlet to 475F outlet, it would be reasonable to have the hot oil leave the exchanger at 525F. Given this hot oil outlet temperature, we would like a hot oil to supply sensible heat via a temperature drop of around 100F, yielding a hot oil supply temperature of 625F. However, if the highest temperature process demand is small, a relatively large flow can be used with a smaller hot oil temperature drop or a smaller approach temperature. For example, a recent Distillate Unionfining unit had a charge heater with a hot oil temperature drop of only 8ºC (15ºF) and an approach temperature of only 5ºC (9ºF). Duty was about 3 MMBTU/hr.

5.2 Heat Transfer Fluids

The term hot oil is typically used to describe the circulating fluid since it is hot and it is derived from a hydrocarbon. A more generic term is Heat Transfer Fluid (HTF) since the fluid may be water based or not very hot at all.

a. Synthetic Heat Transfer Fluids

Synthetic Heat Transfer Fluids are specially created for use in a hot oil system. Their thermal properties are such that they are very stable at high temperatures, and they have fluid properties (such as specific heat, viscosity, vapor pressure, and pour point) that are suitable for the high temperatures incurred in a hot oil system.

HTF thermal stability is a measure of the lifespan of the hot oil. When a HTF is heated to high temperature, it will thermally breakdown into low-boilers and high-boilers. The low-boilers are gaseous compounds that will be vented through the surge drum’s vent to the flare. The high-boilers are heavy liquid and/or solid compounds that will accumulate in the system until purged or filtered. Either way, a highly stable HTF is desired. HTF manufacturers will define a maximum bulk temperature (MBT) for the HTF. Maintaining the heater outlet temperature below this MBT will help assure stability. In addition, the HTF manufacturer will define a maximum film temperature for its HTF’s. The fired heater design will limit the maximum film temperature to a value equal to or less than the manufacturer’s maximum film temperature.

Synthetic HTF’s are expensive. List price (in 2008) for Therminol 66 is about $44 / gallon and will fluctuate with the price of crude. In general, the hotter the hot oil supply temperature, the more expensive the fluid required. Substantially lower hot oil supply temperatures can allow the use of less expensive fluids.

Despite the high capital cost, synthetic HTF’s are the default choice for a Inflection Point Engineering Hot Oil System. Their stability and fluid properties provide better operations and reduced operating costs. Even at low hot oil supply temperatures, the synthetic HTF will be the default since the availability and characteristics of a non-synthetic HTF are not known.

There are multiple manufacturers of synthetic heat transfer fluids. Each manufacturer will market a complete line of synthetic HTF’s. A partial list of the manufacturers and their product most applicable to Inflection Point Engineering Hot Oil Systems is below:

• Solutia Therminol 66
• Dow Dowtherm RP
• Sasol Marlotherm SH

Inflection Point Engineering’s default hot oil is Therminol 66. It has been used in numerous Inflection Point Engineering hot oil systems and has a very good history. While the properties of Therminol 66 are used in the design of the default hot oil system, the Inflection Point Engineering Schedule A should not refer to Therminol 66 or any other synthetic HTF by name. Any of the reputable manufacturers of synthetic HTF’s, including but not limited to the above, should be able to supply a fluid that will work in the Inflection Point Engineering Hot Oil System. The final selection of the HTF is made by the client and will normally be based on economic considerations after considering overall suitability of the various HTF’s.

If the client requests that a specific synthetic HTF be used in the design of the hot oil system, Inflection Point Engineering should verify that that HTF is suitable for the overall service and then use the properties of that HTF for the design of the equipment.

b. Non-Synthetic Heat Transfer Fluids

Non-synthetic HTF’s refer to those fluids readily available inside a particular refinery or chemicals plant. Diesel fuel, for example, would be a non-synthetic HTF.

Non-synthetic heat transfer fluids are sometimes requested by a customer in an effort to save on capital. When the HOST is above 500ºF, an attempt should be made to convince the customer to spend the money for a synthetic heat transfer fluid. Non-synthetic heat transfer fluids can cause numerous problems in operating the Hot Oil System. Heat transfer fluids from some thermal operation, such as visbreaking or coking, typically contain a large amount of olefin, which will polymerize and eventually clog the system. Some non-synthetic HTF’s will have very high sulfur levels such that the metallurgy may need upgrading, which will eliminate any cost saving in using a non-synthetic heat transfer fluid. Non-synthetic heat transfer fluids are not as stable as synthetic HTF’s. The degradation products of synthetic heat transfer fluids mainly tend to form light products that are removed through the pressure regulation system on the surge drum. The non-synthetic HTF’s, on the other hand, tend to form high boiling compounds and coke, which accumulate in the system A purge stream is required when non-synthetic heat transfer fluids are selected to minimize the levels of coke and high boiling compounds.

If the customer insists on using a non-synthetic heat transfer fluid make sure to obtain the following information to allow modeling in 9.8; ASTM D86 boiling point curve, API value, and wtppm (or wt%) sulfur. If the ASTM D86 boiling point curve is not available, obtaining two vapor pressure temperature points is sufficient. Obtaining information such as pour point or viscosity can also be useful.

For HOST’s below 500ºF, a non-synthetic HTF is usually acceptable. Serious operational problems, including product degradation, can typically be avoided. Also, the capital savings associated with not buying a synthetic HTF are usually greater than any operational savings associated with a system using synthetic HTF’s. Above 550ºF, non-synthetic HTF’s have been found to be inappropriate. They have operational problems that outweigh any capital savings associated with avoiding the synthetic HTF’s. With HOST’s between 500ºF and 550ºF, a detailed study should be performed to confirm the suitability of the non-synthetic heat transfer fluid.

5.3 Finalize HOST

After the initial value of the HOST is determined and the hot oil is selected, the HOST can be refined upwards as follows:

• Obtain the maximum bulk temperature of the selected hot oil

• Derate the maximum bulk temperature by 20ºF. The result is the heater outlet temperature (HOT). Inflection Point Engineering derates the maximum bulk temperature in order to extend the life of the hot oil. As a rule of thumb, the fluid life doubles with every 20ºF reduction in temperature.

• Reduce the HOT to reflect heat losses between the heater outlet and the process users. The result is the HOST. A temperature drop of 5ºF is normally selected. This is a conservative value and represents all heat loss from the hot oil system. Generally do not change the temperature drop based on size of hot oil system, but doing so is acceptable with appropriate study.

While the HOST can be refined upwards, there is no requirement to do so. Using a HOST more than 25ºF below the hot oil’s maximum bulk temperature will increase pumping costs and exchanger sizes, but it will also extend the life of the HTF.

The default Inflection Point Engineering hot oil system should be designed for a HOST of 625ºF. The HOT will then be 630°F. For metric jobs, use 330°C (or 626°F) and 333°C (or 631.4°F). This is based on the use of Therminol 66 as the hot oil.

6. PROCESS DESIGN

Process Design of Hot Oil Users

The HOST should be provided to all process users. The process unit process engineers will then define exchanger duties and required hot oil flows

The hot oil temperature drop should be as large as possible to minimize the flow required. However, when hot oil is on the tube side of a shell and tube exchanger, the hot oil T should be no more than 125ºF in a single shell to avoid the possibility of tube sheet distortion and leakage. This limit does not apply to hairpin exchangers since they have an isothermal tube sheet. This limit also does not apply to heat exchangers where the hot oil is on the shell side (for example in vertical thermosiphon reboilers).

An approach temperature (equal to the hot oil outlet temperature minus the process outlet temperature) of 50°F for hot oil heated exchangers should typically be used for functional economic designs. Consult a heat exchange specialist if a lower approach temperature is required and/or consider the use of High Flux Tubing.

6.2 Model the Hot Oil

Use appropriate methods to model the hot oil in 9.8 for use in the process design of the hot oil system.

6.3 Compile Process User Loads

Obtain process duties and hot oil flow rates for the various hot oil users. Determine the total hot oil flow through all heat exchangers based on the process design (typically this is the H&W balance duties which also would be consistent with the heat exchanger specification hot oil flows). Call this flow the Process Hot Oil Flow (PHOF). Determine the total duty through all the hot oil exchangers based on the process design. Call this the Process Duty (PD). Include as a process duty the heat loss in the system resulting from a temperature drop from the HOT to the HOST.

6.4 Bypass

Include in the heat and weight balance a flow of hot oil through a bypass loop. The bypass valve for the hot oil system shall be specified to normally pass 15% of the PHOF. This flow represents hot oil capacity which can be diverted from the bypass to process exchangers to provide additional duty. The valve itself should have a capacity to pass additional hot oil corresponding to excess circulation which would occur at process turndown.

The bypass loop is not a typical “E” assembly. Rather the control valve bypass should be manually sized so it is large enough to pass 60 % of the rated flow of one pump. This allows the pump to be run-in at startup without using the control valve. Adjust if needed based on pump size.

A value of 15% is selected to allow future flow of 5% through the bypass when the individual process users have design flow rates 10% higher than normal flow rates.

6.5 Tempered Hot Oil Systems

In some units, including Sulfolane and Phenol Units, hot oil can be too hot for the process. High temperature hot oil would damage the process fluids. A lower temperature HOST should be defined for this tempered hot oil system. The system is then set up as a mini-hot oil system, complete with circulation pumps, surge drum and headers, but no fired heater. A temperature control valve is used to add heat to the tempered hot oil system by admitting hot oil from the main system. An equivalent flow is then sent back to the main hot oil system

A separate surge drum should be provided for the tempered hot oil system. Use level control to return hot oil to the main system.

6.6 Prepare a Heater Summary

a. Normal Heater Inlet Temperature (NHIT)

Calculate the hot oil return temperature based on the flow weighted return temperature from each exchanger and from the bypass valve. Here, assume that the temperature of the hot oil from the bypass valve is equal to the HOST. The result is the Normal Heater Inlet Temperature.

b. Design Heater Inlet Temperature (DHIT)

Calculate the hot oil return temperature based on the flow weighted return temperature from each exchanger, and assuming the same value for the bypass valve flow (i.e. the bypass flow is assumed to return at the same temperature as the weighted average from the exchangers). The result is the Design Heater Inlet Temperature.

c. Normal Duty

Set the normal duty equal to the Process Duty.

d. Design Duty

Set the heater design duty equal to 115% of the Process Duty.

e. Normal Flow

Set the normal flow equal to 115% of the PHOF.

f. Design Flow

Set the design flow equal to 115% of the PHOF.

g. Heater Outlet Temperature

Set the heater outlet temperature equal to the HOT for both the normal and design cases.

h. Hot Oil Systems with Convection Sections in Hot Oil Service

In some hot oil systems (e.g., for LAB Complexes), some “cold” hot oil is sent to the convection sections of other fired heaters in the complex for overall fuel efficiency reasons. Heat pickup in these convection sections can vary depending on the operation of the fired heaters.

In these cases, determine normal and design duties and flows as follows.

Set normal hot oil heater duty equal to the process duty minus the waste heat pickup.

If the waste heat pickup is less than 20% of the process duty, then set the design hot oil heater duty equal to the 115% of the PD. Take no credit for the waste heat pickup (WHP). This assures that the hot oil system will always have sufficient firing capacity, even if the other convection section is not in service. Some judgment is allowed in this area. If you lose process duty at the same time that you lose the waste heat pickup, then taking credit for the waste heat pickup is probably acceptable. For example, if a Pacol unit charge heater goes offline, the users in the Pacol unit will also likely go offline.

If the waste heat pickup in the other fired heaters is more than 20% of the PD, then set the design hot oil heater duty equal to 115 % of the process duty after subtracting 50% of the waste heat pickup. That is,

Design Duty = 1.15 * (PD- 0.5 * WHP)

Do not take full credit for the waste heat pickup since the amount of waste heat will vary, and it is such a large portion of the total load that you don’t want the hot oil heater to be left undersized.

Set the heater normal flow equal to 115% of the PHOF minus the design flow of hot oil through the convection section(s).

Set the heater design flow equal to 115% of the PHOF minus the design flow of hot oil through the convection section(s). Thus, normal flow will equal design flow.

The above assumes that the convection section is in parallel with the hot oil heater. That is, “cold” hot oil at the NHIT or DHIT is sent to the inlet of the convection section and “hot” hot oil leaves the convection section at the HOT. Consult the hot oil specialist if the convection section is in series with the Hot Oil Heater.

6.7 Purge Stream and Makeup

For systems with non-synthetic HTF’s, include a purge stream and makeup stream in the process design.

Purge and makeup rates must be calculated for each individual job. See Hot Oil Specialist for support.

For an initial estimate, assume that the purge stream flow rate equals the makeup stream flow rate. Set these equal to 1% of the PHOF. This is about what is typically needed to achieve a turnover of hot oil of one system volume per day.

7. PFD and MSD

A Process Flow Diagram (PFD) should be prepared to indicate the process flow of the hot oil system. All major equipment should be shown on the PFD. Supply and return lines should be shown going to/from each hot oil user. The pumpout cooler does not have to be shown on the PFD. If it is, it should be shown independently of the main hot oil system.

The PFD should be consistent with the future P&ID’s and system hydraulics. See Section 8 for more details. This will minimize problems later on in the project.

A PFD module for Hot Oil Systems is available in the documentation system. See drawing P99020-0-A1.

Similarly, prepare a Material Selection Diagram (MSD) as required.

8. HYDRAULICS

The hot oil headers and individual supply/return pipes shall be sized for 1.5 psi/100 feet maximum pressure drop and 700 ft/min max velocity. Pressure drop criteria usually governs pipe sizing.

There are two main methods of setting up hydraulics for a hot oil system. See below for descriptions. Either method is normally acceptable at both the process and project engineering stages. This is because the detailed layout of the heat exchangers and the process units are not yet known, and the Inflection Point Engineering engineer is forced to make some assumptions. However, we still want to make reasonable assumptions such that equipment installed per Inflection Point Engineering project specifications will have enough flexibility to provide a good, operable system once the plant is started up without burdening the system with tremendous utility waste due to excessive pressure drops across control valves.

While either method is acceptable, the “Assume All Users Are Supplied From a Common Node” method is preferred.

Whichever method is used, the same method should be used for both the process and project stages. If the method is changed in mid-project, the PFD should be revised.

8.1 Assume All Users Are Supplied From a Common Node

In this case, the supply pressure is the same for all users as is the return pressure. The only variations in pressure drop across individual user control valves will be a result of variations of heat exchanger pressure drops and/or individual supply pipe pressure drops.

For process hydraulics, assume that the supply and return headers each have pressure drops of 25 psi. See section 8.3 below for additional assumptions.

For project hydraulics, first size the headers and calculate the actual pressure drop per 100 feet of piping based on the actual pipe diameter and flow at the start of the header. Next, determine a header length appropriate to the project based on detailed or typical plot plans. The header length should be the distance to the farthest user to assure adequate pump head. Multiply the actual header length by a factor of 2.0 to obtain an equivalent length. All the users, including the bypass, are then at this distance from the start of the header. If a suitable plot plan is not available, choose an equivalent length such that the pressure drop is 25 psi in each of the supply and return headers.

A variation to the “Common Node” method is assuming that the process users in different process units are supplied from a common node, but there is a different node for each process unit. This could be useful for cases where the process blocks are at widely different distances from the hot oil heater.

8.2 Assume Users are Sequential

For process hydraulics, assume that the supply and return headers each have pressure drops of 25 psi. Assume no pressure drop between users during process stage. Pressure drop will be reflected in project stage. See section 8.3 below for additional assumptions.

For project hydraulics, arrange the take off of supply from the hot oil header to the various hot oil users in a suitable manner. This may be based on a detailed plot plan. If no plot plan is available, place users along the header as desired, but making sure that all users from a single unit are sequentially ordered.

Near the hot oil heater, the supply pressure for each process user will be high. Away from the hot oil heater, the supply pressure will be lower due to pressure drop in the supply pipe. Similarly, the pressure will drop in the return header. The result is that exchangers at the beginning of the hot oil system will have an associated control valve with a larger pressure drop.

When using this method, it may seem desirable to increase pipe size for exchangers at the ending of the hot oil system so that the piping pressure drop is reduced and the associated control valves have a larger pressure drop (similar to the ones at the beginning of the hot oils system). Doing this could allow the pump head to be reduced. However, the temptation to do so should be resisted during the Schedule A stage. Stick to the normal pipe sizing rules. The option of increasing the pipe size should be left to the detailed engineering contractor in the event the final layout leaves the particular control valve with limited pressure drop.

If no other information is available, assume a length of 600 feet from the hot oil block battery limits to the first user. Assume 200 feet of straight pipe between each user.

Alternatively, assume that all process users for a single process unit come off the header at essentially the same point. Assume a length of 500 feet from the header to the first process unit. Allow 10 feet of pipe between each user in the same process unit. Allow a length of pipe between process units equal to 50 feet plus one half the sum of the widths of the two adjacent process units.

8.3 Either Method

For the process hydraulics, assume, as a default, a P of 25 psi for individual exchanger control valves. Assume a pressure drop of 5 psi for the piping and flow meter. Assume 10 psi for heat exchangers, ignoring for now the number of shells and whether or not the hot oil is on the shell side or tube side.

Alternatively, if the BEDQ provides the supply and return header pressures, then adjust the control valve pressure drop as needed assuming a 15 psi drop in the exchanger and piping.

For project hydraulics, each process user should be modeled individually. Modeling should include the supply pipe, the flow meter, the control valve, the heat exchanger, and the return piping. Pressure drops through the individual control valves should be at least 25 psi for the normal case and at least 10 psi for the design case (typically 110% of normal). Set the pipe length of both the supply and return pipes equal to 50 feet plus one half the sum of the process block width and length. Use typical Inflection Point Engineering equipment layouts / dimensions if detailed plot plans are unavailable.

The size of the hot oil system is such that it is not always possible to model the entire supply and return headers using a single circuit. In this case, attempt to model the supply header and return headers in separate circuits. Use a dummy node for the end of the supply header. Adjust the pressure of the dummy node as needed to achieve desired pressure drops in the individual exchanger control valves.

For process hydraulics, assume a pressure drop of 50 psi in the hot oil heater. For project hydraulics, use actual pressure drop if determined by the fired heater specialist during the design of the hot oil heater. Model pressure drops in heater supply and collection manifolds as required. In particular, model the globe valve upstream of the heater with a pressure drop of 10 psi. Normally, a globe valve should have a pressure drop of 5 psi. The extra 5 psi is a fudge factor reflecting the static head lost in the hot oil heater since the inlet elevation is not equal to the outlet elevation and the specific gravities are different. The 5 psi fudge factor can be recalculated for a specific job as desired. See the Hydraulic Specialist for assistance in completing system modeling if required.

For process hydraulics, assume a pressure drop of 10 psi for all the miscellaneous piping in the hot oil unit’s battery limits. For project hydraulics, use normal procedures to model the hydraulics from the surge drum to the pumps, from the pumps to the heater, from the heater to the battery limits, and from the battery limits to the surge drum. The supply and return headers would then start / stop at the battery limits. Include hot oil pipes to a sidestream filter, parallel convection heaters, or hot oil system users as required.

Set up both process and project hydraulics with an operating pressure of 25 psig at the top of the surge drum. On rare occasion, this should be modified as needed based on the hot oil vapor pressure or the flare header back pressure.

For project hydraulics, complete the three typical cases: normal, design, and turndown. For the bypass loop, normal flow through the control valve should be equal to 15% of PHOF. For the typical 110% design case, flow through the control valve should be equal to 5% of the PHOF. For the typical 60% turndown case, flow through the control valve should be 55% of the PHOF. It is noted that flow through the pump(s) and hot oil heater should be the same for all three cases.

When issuing the Process Hydraulics Report, EDI Section C.1, report only those circuits inside the scope of the Hot Oil System Schedule A itself. That is, do not report the supply of hot oil to the individual users of hot oil in the various process units. Delete these from Report C produced by the hydraulics program. These circuits are reported in the appropriate process unit EDI.

8.4 Single Process Unit Hot Oil System

In the event a hot oil system is installed in a single process unit, model the hydraulics based on the generic Inflection Point Engineering plot plan for that process unit. Consult the Plot Plan specialist to locate the hot oil heater and heat exchangers if not shown. Use the “Assume Users are Sequential” method. Reduce header pressure drops to 5 psi for process hydraulics.

P&IDS

The P&ID’s for a specific Schedule A should be based on the hot oil modules. A listing of the modules is as follows:

F990003		Cause and Effect Table
F990005		Hot Oil Supply
F990010		Hot Oil Surge Drum
F990015		Hot Oil Heater
F990020		Circulating Hot Oil Header
F990025		Circulating Hot Oil Header

In most cases, Inflection Point Engineering Project Specification 697 will be used to detail fuel firing requirements so additional P&ID’s for heater firing are not required. In cases where the 697 is not used for a particular project, then heater firing and air preheater P&ID’s should be included as required. P&ID’s for detailed fuel systems should be developed on a case by case basis, starting from the heater firing modules.

Specific Details

Include a drum filling rack on the hot oil supply P&ID. The rack should typically be specified to hold five drums.

Supply of Hot Oil to Users

As can be seen in the hot oil modules, the Hot Oil System Schedule A stops right after a block valve on the supply header and begins again right before a block valve on the return header. Piping, instrumentation (flow meters and controls valves), and the heat exchangers are inside the scope of the various process units. Two exceptions to this are when the hot oil system is a user of hot oil (say for a fuel gas heater) and when the hot oil system is dedicated to a single process unit and included in the same Schedule A.

The proper arrangement, in sequential order, for the supply of hot oil to a process exchanger is as follows:

Supply Header	Shown in Hot Oil Schedule A
Isolation Valve	Shown in Hot Oil Schedule A
Supply Pipe	Shown in both Hot Oil and Process Unit Schedule A’s
Flow Meter	Shown in Process Unit Schedule A
Control Valve	Shown in Process Unit Schedule A
Heat Exchanger	Shown in Process Unit Schedule A
Return Pipe	Shown in both Hot Oil and Process Unit Schedule A’s
Isolation Valve	Shown in Hot Oil Schedule A
Return Header	Shown in Hot Oil Schedule A

The above arrangement is mandatory unless alternate provisions are made to relieve hot oil from the individual exchangers for a fire case. The above arrangement, with a Locked Open isolation valve on the return pipe, assures that there is a free path from the heat exchanger to the surge drum. The relief valve on the surge drum then protects the various heat exchangers throughout the plant. If the control valve is placed on the downstream side of the heat exchanger, then it must be assumed that the control valve will fail closed, and the free path is now blocked for the fire case. It should be noted that the tube rupture case is not affected by the location of the control valve, i.e. whether it is upstream or downstream of the heat exchanger. It would be a double contingency to design for both a tube rupture and a control valve fail closure.

As noted, block valves on the return pipe from individual users shall be marked as Locked Open on the P&ID.

9.3 Bypass Control

In most cases, the control valve in the bypass loop shall be an FV with the flow meter controlling the flow just upstream of the fired heater. The intent is to maintain constant flow through the fired heater.

In some cases, the control valve in the bypass loop shall be a PDV. In these cases, include a board mounted differential pressure indicator/controller around the PDV. The primary time when a PDV should be used instead of a FV is when the hot oil system contains a process unit heater with its convection section in hot oil service and that convection section has a very high pressure drop. In that case, a control valve is put just upstream of the hot oil fired heater to increase pressure drop in the main hot oil loop. Without the control valve at the hot oil heater, liquid will not flow through the process unit heater convection section at the desired rate. This control valve will be an FV with the flow meter controlling the flow just upstream of the control valve. The control valve shall have a limit stop and shall be fail open.

10. PROJECT SPECIFICATIONS

Complete the project specifications for the Hot Oil Schedule A as required. Some details for specifying the various equipment items are noted below. Except as noted, the information below applies to systems using synthetic HTF’s. Specifications should be modified as appropriate for systems using non-synthetic HTF’s.

10.1 Surge Drum

Complete a 301 Specification for the Hot Oil Surge Drum. Use the Inflection Point Engineering Vessel Design - Program 254. Model the Hot Oil Surge Drum as a normal surge drum.

a. Flanges

Flanges on the bottom of the vessel, i.e. below the normal liquid level, shall be Class 300. Class 300 flanges are needed to minimize leakage due to low surface tension of synthetic HTF’s. Flanges on the top of the vessel, i.e. in the vapor space, can be Class 150, if Class 150 flanges are otherwise acceptable.

b. Pump Suction and Inlet Nozzle

For systems with synthetic HTF’s, the pump suction nozzle will be in the bottom head. For systems with non-synthetic HTF’s, the pump suction nozzle should be on the side of the drum, a minimum distance above the bottom tangent line. The side suction nozzle is desired to allow solids to settle to the bottom of the surge drum. These solids would then be purged at regular intervals. Include a bottom head drain for systems with non-synthetic HTF’s.

For all HTF’s, the inlet nozzle will be on the side of the vessel. Allow the 254 program to set the height above the tangent line. It is acceptable to have the nozzle not totally submerged at startup; there is no need to put in additional hot oil (see next item). During normal operation the nozzle will be submerged.

c. Sizing

The surge drum is sized to allow thermal expansion of the hot oil and to provide expansion volume in the event of a tube rupture, if needed. For systems with synthetic HTF’s, select a tangent length based on the sum of the following:

• An allowance of 3 feet in the surge drum to permit pump operation when the system is filled and the heat transfer fluid is cold.

• Enough tangent length to allow for thermal expansion of the entire hot oil volume from low ambient temperature to the heater outlet temperature.

• Enough additional tangent length to accommodate a tube rupture. Volume in the surge drum will equal the volume of the piping (both return header and lateral pipe) from the most distant heat exchanger with a tube rupture case.

• An allowance of 4 feet of tangent length at the top of the surge drum to allow for liquid disengaging in the event of a tube rupture.

Use T-900-03, Hot Oil Surge Drum Tool, to size the Hot Oil Surge Drum. This tool will require as input information on the heat exchangers, piping, and heater. It will then calculate the surge drum volume as required.

T-900-03 allows two different sizing options. First, for the tube rupture case as mentioned above. Second, for small systems, the hot oil surge drum can be sized to hold 100% of the hot oil in the system. Sizing the drum to hold all the hot oil can allow the client to avoid use of drums/barrels and makes unit shutdown/startup simpler. For larger systems, though, the increased drum cost would be high and is usually not economical.

Select a surge drum diameter as required, typically to maintain an L/D ratio of approximately 3:1. For systems with non-synthetic HTF’s, the allowance of three feet for cold pumping should be measured from the top of the pump suction nozzle.

When sizing the surge drum, densities from 9.8 should not be used for synthetic HTF’s. The accuracy of the 9.8 model is very poor at ambient temperatures. Instead, use vendor information for properties at both low and high temperatures.

d. Operating pressure

Set the operating pressure at the top of the surge drum at 25 psig for most hot oils. If the vapor pressure of the hot oil is greater than 0 psig at the NHIT, set the operating pressure equal to the vapor pressure plus 25 psi.

e. Design Pressure and Temperature

The surge drum is typically designed for a minimum internal design pressure of 50 psig at a temperature 50ºF above the HOT. Design the drum for full vacuum at the NHIT.

f. Orientation and Elevation

Use a vertical surge drum. NPSH concerns are normally not an issue for hot oil systems with synthetic HTF’s and a gas blanketed surge drum so typically design the vessel elevation based on minimum clearance requirements. Elevate the vessel as needed if NPSH required dictates.

g. Multiple Surge Drums

In the rare event that a hot oil system requires two surge drums, the surge drums should be made identical. Piping to and from the surge drums should be symmetrical. Drums should use common pumps. Consult the Hot Oil Specialist if more than two surge drums are required.

h. Sumps

Some clients request hot oil sumps – that is, underground storage pits - to allow the hot oil from exchangers to be quickly drained and stored. Do not specify these sumps in the Schedule A. Inflection Point Engineering does not think they are necessary. They entail considerable expense, and they may cause degradation of the hot oil. If client decides to include them, however, Inflection Point Engineering should not object.

10.2 Hot Oil Storage Tank

Inflection Point Engineering does not require the installation of a hot oil storage tank. If requested by the client, it should be outside the scope of the Inflection Point Engineering Hot Oil System Schedule A. See the tankage specialist if a hot oil storage tank is required.

For smaller hot oil systems, the hot oil surge drum can be increased in size to hold 100% of the hot oil in the system. See above.

10.3 Hot Oil Circulation Pumps

Specify two pumps (one normally operating, one spare) unless the system is so large that a single operating pump cannot be used. Motor drivers are typically specified. In very cold weather locations, having one pump with a turbine driver can be considered to reduce likelihood of the hot oil becoming too viscous in event of an extended power outage.

While there are advantages to specifying three pumps (two normally operating, one spare), this shall not be specified except as requested by client or for those cases when the pump size does not allow only two pumps.

Specify pumps such that rated flow equals normal flow. Generally, set rated flow equal to 115% of PHOF. For complexes with convection sections in hot oil service, increase rated flow, as necessary, to reflect flow through the convection section. Pump rated head will be provided in the detailed hydraulics.

Include autostart of spare pump only if requested by the client. Decision to add autostart should be independent of the number of operating pumps. That is, having 2N/1S pumps does not justify having autostart if having 1N/1S did not justify autostart.

When there are more than two normally operating pumps (for example, if there are four pumps, three operating and one spare), each pump shall be provided with individual flow meters.

a. 501 Specification Details

Specify API Primary Seal Flush Plan 23 for the circulation pumps. Specify X-Y proximity vibration monitor probes. Specify resistance temperature detectors (RTD’s) to monitor bearing temperatures when rated power is greater than 500 hP.

Motor note M5 is not typically required as there is a control valve on the discharge. A note should be required to reflect that the motor need not be oversized for low temperature startup since the flow would be reduced at startup.

Ensure that the maximum viscosity is shown in the specification. This is the viscosity at either the minimum ambient temperature or the heat tracing temperature, whichever is lower. Also provide viscosity at 120°F for API Plan 23.

b. Non Synthetic HTF’s

Specify the pump rated flow equal to pump normal flow. Set rated flow equal to the sum of 115% of the PHOF and the maximum purge flow. For complexes with convection sections in hot oil service, increase rated flow, as necessary, to reflect flow through the convection section.

Check for operating conditions that may cause the surge drum (pump suction), to exceed the autoignition temperature of the material being used. This situation usually occurs in systems that have large intermittent flows or when turndown flow is less than the fired heater minimum flow. If autoignition is a possibility include unpressurized dual seals on the pump specification and plan “TL” on the P&ID. Consult with the pump specialist assigned to the complex to insure all the correct notes have been added to the specification.

10.4 Additional Pumps

Besides the hot oil circulation pumps, the following two pumps are typically required.

a. Pumpout Pump

A pumpout pump is specified to remove hot oil from low spots in the system. Size the pumpout pump for a rated flow of 20 gpm and 40 psi of head. This pump is skid-mounted. Normally only one is specified. Add the following note to the pump specification, “Pump may run dry for a period of 5 minutes up to ten times per year”. This pump can also be used to add hot oil to the hot oil system from small drums in the drum filling rack.

b. Transfer Pump

A single transfer pump is specified to allow initial fill (or later emptying) of the hot oil. Hot oil will be pumped from an iso-container or an offsite storage tank. Size this pump to fill (or empty) the hot oil system in about one day. Set rated head equal to the head of the hot oil in the hot oil heater plus 10 psi.

In some cases, fuel pumps or tempered hot oil pumps are required. Specify as required.

10.5 Fired Heater

Base the fired heater design on the following.

	DESIGN
Hot Oil Flow Rate	1.15 x PHOF	1.15 x PHOF
Target Pressure Drop - psi	50	50
Inlet Temperature	DHIT	NHIT
Outlet Temperature	HOT	HOT
Duty	1.15 x PD	PD

For metric jobs, use a target pressure drop of 3.5 bar (50.75 psi) or 3.5 kg/cm2 (49.78 psi) as appropriate for the job specific units.

See section 6.6 for details on designing fired heaters if there are convection sections in hot oil service. An appropriate heater specification (normally a 202 specification) will be created by the heater specialist. For large hot oil systems, an air preheater system is usually included.

When a 202 specification is prepared, the heater specialist may estimate actual heater pressure drop. If estimate is not prepared, then 202 specification will just show the target pressure drop noted above.

If pressure drop is estimated, and if the estimated pressure drop is within the range of 45 psi to 52 psi, then include the target pressure drop in the 202 specification. If the estimated pressure drop is outside this range, then adjust the overall system design to reflect estimated pressure drop and make sure the pump and fired heater specifications and hydraulics reflect actual estimated heater pressure drop.

Consult hot oil specialist if a 201 specification is required.

The design pressure for the hot oil heater is the shutoff pressure of the hot oil circulation pump.

For heaters with synthetic HTF’s, set the maximum film temperature equal to the maximum film temperature as defined by the HTF manufacturer.

Set the maximum design heat flux rate equal to 12,000 BTU/hr-ft2.

If required, include a 965 project specification for the Fuel Gas Preparation System. See also Section 11, Fuel Systems, below.

10.6 Heat Exchangers

The various users of hot oil will be specified in the appropriate process unit Schedule A. While technically part of the hot oil system, they are not considered to be part of the Hot Oil Schedule A. Note that the process unit heat exchangers should be specified with a design pressure equal to the shutoff head of the hot oil circulation pumps.

Complete a 401 Specification for the exchangers listed below. Additional heat exchangers may be required for the fuel gas system, if not covered by the 965 specification, and for the waste gas/liquid fuel systems.

a. Systems with Synthetic HTF’s

Provide a hot oil pumpout cooler to cool the hot oil before removing it from the system and loading it into storage drums. This exchanger is sized to cool 20 gpm of hot oil from the normal surge drum operating temperature to 120˚F using cooling water. Note that the flow rate should be consistent with the pumpout pump. Refer to Procedure for design temperature and pressure guidelines.

On occasion, a customer may request a startup heater whose purpose is to warm up the hot oil to make it less viscous and more pumpable. A startup heater is not typically included and should generally be specified only at the request of the customer (see exception below). With the request should come a basis for sizing the heater. If no basis is given, use the following:

• Use LP steam
• Locate the heater in the surge drum
• Make the startup heater as big as it can be given the diameter of the Hot Oil Surge Drum

In locations where it is so extremely cold that the minimum ambient temperature is less than the pour point of the HTF, Inflection Point Engineering should add a startup heater unless the customer asks for it not to be installed. The design basis is as follows:

• Use LP steam
• Locate the heater just downstream of the hot oil heater in between the supply and return headers
• Set duty equal to the heat loss due to drop in temperature from the HOT to the HOST. See Section 6.3.

Adjust the above bases as needed. It is noted that if doing initial fill during cold weather, the customer will need to keep HTF warm (for example by storing in a heated warehouse) prior to initial fill and then get the startup heater in service as soon as possible.

Use the process specific package in ABE, and Tool to import information for the pumpout cooler and startup heater.

Because of high swings in viscosity when cooling or heating synthetic hot oils, it may be necessary to complete special HTRI runs as noted in the 401 Calc Tool. See a heat exchanger specialist if the 401 Calc Tool indicates this need.

b. Systems with Non-Synthetic HTF’s

Non-synthetic HTF’s will normally be turned over rapidly so that average residence time in the system is small. A heat exchanger is needed to cool down the purged HTF and another may be desired to warm up the makeup HTF.

In general, provide a make-up/purge heat exchanger to warm up the cold incoming HTF while cooling down the hot outgoing purge stream. This exchanger is similar to a feed/bottoms exchanger. Sizing is based on required purge rates and the NHIT.

Provide a purge cooler to lower the temperature of the purged HTF to the desired battery limit temperature. Depending on the duty, battery limit temperature, and/or customer requirements the purge cooler can be water cooled, air cooled, or a combination of an air cooled followed by a water cooled exchanger. As a default, provide an air cooled exchanger followed by a water cooled exchanger. If a battery limit temperature is not provided, assume it is equal to the high ambient temperature.

The purge cooler also serves as a backup to the make-up/purge exchanger to insure the battery limit temperature is not exceeded. The design duty is the duty required in cooling the purge stream from the NHIT to the battery limit temperature. Set the design temperature of the purge cooler equal to the NHIT.

Both of these exchangers will be operated continuously.

Provide a startup heater if requested by the customer. Use the guidelines given above for synthetic HTF’s.

10.7 Pressure Relief Valves

There are typically only two relief valves that must be reported in the 807 specification. While there may also be relief valves in other services, these are normally specified by others (See IPE-TM-800-06, “Pressure Relief Valves ‘By Others’”). If fuel system vessel specifications are included in the Schedule A, then include relief valves for those services as required.

a. Hot Oil Surge Drum

A relief valve shall be installed on the top of the surge drum, typically discharging to the relief header. A balanced bellows valve is usually required because the total back pressure is usually greater than 10% of the set pressure. There are typically two relief cases.

(1) External fire

Size valve for a fire under the surge drum itself. Use Tool T-807-04 with inputs as follows for a typical synthetic HTF.

Relief temperature 795ºF

Z 1

k 1

Latent heat 86.3 BTU/lb

Vapor Molecular Weight 252 lb/mol

(2) Tube Rupture

Size valve for tube rupture case of any heat exchanger using the normal procedures given in Procedure . Check to see if any liquid process fluid going into the hot oil system will flash at hot oil temperature and surge drum accumulated pressure and size the relief valve to relieve the flash vapor.

When determining if any liquid will flash, assume that the liquid is insoluble in the HTF. This is the conservative basis. In some cases, say benzene leaking into Therminol 66, the benzene will likely be soluble to a large extent. However, the extent is unknown and it is likely that the Therminol 66 will quickly become saturated with benzene if in fact the Therminol 66 was not already saturated based on earlier tube leaks or normal thermal degradation.

Also, ignore any heat of solution that might result from a tube rupture.

A third case, failure of the nitrogen pressure control valve in an open position, should also be considered, but it need not normally be listed as a separate case in the 807 specification except for small surge drums in systems without heat exchangers that would otherwise create a tube rupture case. Instead, add a note to say the case was considered but not found controlling.

Include in the 807 specification a note similar to the following, “Fire case relieving rate does not include loads generated in hot oil exchangers. Contractor to determine exchangers’ contribution once their dimensions and location within the fire zone is known.”

b. Hot Oil Heater Outlet

Size the relief valve at the outlet of the hot oil heater for a blocked in – thermal expansion case. Use rules in IPE-TM-807-04, Attachment 6. Use normal heater duty. The use of design duty is not required. Use the specific heat at the normal heater outlet temperature.

The hot oil heater outlet relief valve should have a set pressure equal to the design pressure of the fired heater. A note should be added to have contractor adjust set pressure as required based on elevation of the relief valve. The relief valve outlet is normally piped to the top of the hot oil surge drum. A balanced bellows valve is normally required because of the higher back pressure.

Care should be taken to assure that the relief valve outlet flange rating, the outlet piping pipe class, and the flange rating on the surge drum nozzle are consistent.

10.8 Chemicals

Complete the 106 specification using the Project Specification 106-990E or 106-990M templates.

a. Heat Transfer Fluid

Calculate the volume of hot oil required based on system volume equaling combined volume of pipes, heat exchangers, and fired heater plus the volume in the bottom head and 3 feet (or more for non-synthetic HTF’s) of tangent length of the hot oil surge drum. Add an allowance of 10% and report the result in the 106 specification.

Use Tool to calculate the hot oil volume.

For synthetic HTF’s, no changes in the wording of 106-990 templates are required. For non-synthetic HTF’s adjust the wording as required to reflect actual fluid used.

In general, do not use the name of the actual brand name of the synthetic HTF in the 106 specification or any other project specification. That is, do not state, for example, “Therminol 66”. Calling out a specific make of hot oil will invariably cause questions from one group or another in later stages of the project. Even if the BEDQ lists a specific brand of hot oil, use the generic term “Heat Transfer Fluid” in the project specifications.

b. Nitrogen Consumption

Normal nitrogen consumption is zero. Size the maximum continuous nitrogen consumption rate based on T-616-02.

Calculate startup nitrogen volume requirement based on the following:

• Four purges from 0 psig to 15 psig
• System volume equal to the combined volume of pipes, heater, exchangers, and surge drum

Use T-900-03 to calculate the volume requirement. Calculate maximum startup nitrogen rate assuming each purge is done in 30 minutes.

10.9 Sidestream Filter

All heat transfer fluids will degrade with time. When the solids content of the hot oil gets high, degradation results more rapidly as the solids act as initiation points for future solids content growth. To remove the solids, a sidestream filter is used.

Use templates 912-990E or 912-990M to specify the sidestream filter.

Provide a sidestream filter if a non-synthetic HTF is used. It is not necessary to always include a 912 specification in the Schedule A for systems using synthetic HTF’s. A properly designed and operated hot oil system using synthetic HTF’s should not experience the need for filtration for many years. The base case is to only include, on the P&ID, valved connections for the future addition of the sidestream filter. This reduces upfront capital expense. However, if the customer requests that a sidestream filter be provided, then provide it.

The sidestream filter should be sized to handle a mass flow rate equal to 1% of the rated pump capacity. Do not add additional pump capacity for flow through the filter. Flow through the bypass will be reduced as required during filter operation.

10.10 Piping and Strainers

Provide an 801 project specification (Piping). All hot oil piping which is normally filled with hot oil shall be pipe class MS-22. Even though Class 300 flanges are not normally required based on pressure/temperature, the more robust Class 300 flanges are desired to minimize leaking potential, particularly for smaller pipe sizes since there are more bolts in the Class 300 flanges. Hot oil piping that usually does not contain hot oil can be pipe class MS-21. MS-21 calls for Class 150 flanges.

The 801 specification shall call for flexible hose for use in loading/unloading hot oil from the hot oil system. Hose shall be stainless steel with quick connects and double end shutoff.

Provide an 806 project specification (Strainers). In addition to normal strainers for pumps and fuel lines, include a basket type strainer for the sidestream filter. This strainer shall have 100 mesh / 127 micron wire cloth.

Use Project Specification templates 801-990 and 806-990 to specify the piping and strainers, respectively.

10.11 Miscellaneous

Process specific Project Specification Templates for the following specifications are available in the documentation system.

• Inflection Point Engineering Review of Detailed Design 111-990
• Equipment List 112-990
• Safety Equipment 903-990
• Test Methods and Sampling Schedule 934-990

Include these specifications in the typical Schedule A. Other project specifications should be added as needed.

11. FUEL SYSTEM

The Hot Oil Heater will, of course, require a source of fuel and normal fuel firing equipment. The Schedule A should reflect the fuel requirements for the Hot Oil Heater as would be done for other heaters. See Procedure ” for details.

Complexes with hot oil systems will often not have any heaters other than the Hot Oil Heater. At the same time, these complexes may produce a number of waste gases or liquids. In some cases, non-fuel homes for these waste streams can be defined. In many cases, however, the optimal method for the disposal of these waste streams is through incineration in the hot oil heater.

Streams requiring incineration should be defined as early in the Process Engineering stage as possible. The PFD’s should reflect all waste streams, including pressure, temperature, flow rate, and composition. As the project develops, the flow rates and other characteristics may change so that the Project Engineer will need to update as needed.

When waste fuels are to be incinerated in the hot oil heater, the design of the fuel system becomes much more complex. Design must be considered on a case by case basis. Extra equipment is often required. Some special design considerations are noted below.

11.1 Waste Gases

a. Waste gases are often produced at low pressures. This may force oversizing of lines from the process unit to the hot oil heater to minimize pressure drop. Low ΔP control valves may be specified. Special burners may be required to combust the gas at low pressures. The gases may or may not be combined with normal ‘high pressure’ fuel gas. If they are not combined, segregated burners or special injection connections are typically required.

b. Waste gases may have high liquids content. A special coalescer may be necessary to remove liquids before sending the gas to the heater. Prepare a 913 Project Specification as required. Coalesced liquids should be routed to an appropriate location.

c. Waste gases may be high in sulfur content or may include other undesirable components. The heater should be designed appropriately.

11.2 Waste Liquids

From a hot oil system perspective, waste liquids would ideally be sent to slop or some other location beside the hot oil system. When waste liquids from multiple sources are sent to the hot oil system individually for disposal by combustion, they must be combined in a mixing drum and then pumped to the heater. A drum and pumps are required. The drum would be vented to the heater or some other appropriate location. When liquid laden waste gases are also produced, it is typical to send both the waste liquids and waste gases to a common coalescer, with pump suction off the bottom of the coalescer. Prepare a 913 Project Specification as required.

If waste liquids are sent to the hot oil system as a single stream, they can be treated as a relatively normal fuel oil stream, although the material composition of the waste liquid will likely merit special attention and the quantity available may require that another fuel system provide the bulk of the firing duty.

11.3 Vent Gases

Vent gases differ from waste gases in that they are too low in pressure to be combusted in the normal burners. Total heat released through combustion of the vent gases must be limited to maintain control of fuel firing. The Heater Group should be consulted to confirm that the heat content of the vent gases is not too high.

A detonation arrestor should be included in vent gas lines to the heater. Prepare a 920 Project Specification if vent gases are combusted in the hot oil heater.

An emergency shutdown system should be provided to cut off flow of vent gases to the heater box in the event that the heater is shutdown. The shutdown system should consist of a set of block valves with bleed to atmosphere upstream of the valves. The shutdown system should be SIL 2.

APPENDIX 1 LAB Complex Supplemental Design Information

A.1 The default hot oil to use in LAB Complexes is Solutia’s Therminol 66. Other hot oils have been used in LAB Complexes, such as Dow’s Dowtherm RP and Sasol’s’ Marlotherm SH, but the majority of customers use Therminol 66. For new designs, the customer should advise Inflection Point Engineering of the final selection of vendor before work is started. A few customers have used a non-synthetic hot oil, in particular the heavy alkylate product from the LAB Complex, but the use of this oil requires a special design. Consult with both the Hot Oil and LAB Specialists if customer insists on a non-synthetic oil.

A.2 See LAB Specialist for appropriate Hot Oil 9.8 Model to use. Also consult with LAB Specialist for the appropriate information to characterize the hot oil’s properties.

A.3 When compiling duties and flows for the process users, be aware of inputting the appropriate loads without the duplication or extraneous addition of overlapping duties. The two examples are from the Detal unit: (1) Only use 1 of the 2 interheaters as input as only one of the two exchangers is in service at a time. (2) The regenerant feed and effluent heaters work in tandem. As heat is added to the feed heater, this amount reduces the load at the effluent heater, albeit there is a significant time delay. Typically the overlap of these exchangers is not added to the design of the hot oil system, but rather the overlap is assumed to be within the margin of the system. If the possible overlap becomes a significant portion of the margin, then consult with the LAB Specialist.

A.4 Most LAB Complex have units arranged on the plot such that the hot oil headers must make a major divide and therefore the headers are not one continuous line but 2 or more. This adds a complication to the expectation that the bypass flow should go through a bypass line at the end of each divide. Ideally the flow through each of these bypasses should be the same prorated margin as through the single combined bypass (e.g. a 50/50 split in the main PHOF and for a 15% margin would mean the total flow through each bypass would be 7.5% of the PHOF.)

However, since the plot layout is not set until contractor selection, Inflection Point Engineering makes no changes to its basic design. The above is then for information only during the Schedule A phase of the project. During detailed design, the contractor can add a split ratio controller for each bypass control valve, each of which will need to be an FIC control valve. The same prorating applies to the startup line used to run-in the hot oil pumps.

A.5 “Cold” hot oil from the pump discharge is typically passed through the convection section of the Pacol Charge Heater for heat conservation and the heated hot oil is added to the hot oil supply header. Albeit small, the duty and hot oil flow should be included as part of the normal design duty supplied by the hot oil system. This means the flow and duty to the hot oil heater is reduced accordingly to keep the system balanced at normal conditions. Therefore the correct information for the conditions at the Pacol Charge Heater convection section is required to correctly complete the hot oil process work.

A.6 The hot oil project engineer should inform all hot oil users within the LAB Complex of the final hot oil system’s design pressure as determined from the hot oil pump shut-in pressure. This design pressure will be used to set the design pressure of the hot oil exchangers. Though the engineer of an LAB unit (Detal for example) may have a case where the 10/13th rule will override this design pressure value for a specific exchanger, this overriding value should not be used as the governing design pressure for all the other exchangers. Reasoning; though all the hot oil exchangers share a liquid hydraulic link on the hot oil side, the tube rupture for this override design pressure case is assumed to move down the return header and not affect the other exchangers connected to the return header.

A.7 Though not shown on the Hot Oil System’s P&ID, when hot oil is exchanged in the convection section of another heater (e.g. the Pacol Charge Heater), a relief valve is also required at the outlet of the convection section and shown on that unit’s drawing. However, the destination of this relief valve is also directed to the Hot Oil Surge Drum and needs to be shown on the Hot Oil System’s drawing. Note; exceptions have been made to allow the discharge of this relief valve to be directed to the return header due to the length of this line.

A.8 Though we are trying to avoid favoritism by not listing vendors, we have made exceptions by listing “Suppliers” information (such as that for Solutia Dow, and Sasol) at the bottom of the 106 specification. This should only be done if specifically requested by the client.

A.9 Include a temperature indicator on the hot oil return pipe downstream of each heat exchanger using hot oil. This temperature indicator should be shown in the Process Unit Schedule A.