Fired Heater Fuel System Design

1. Table of Contents

Attachments

Figure 1 -- Liquid Heats of Combustion

Figure 5 – Project Specification 301

2. Purpose

This procedure describes the process of and guidelines for designing fuel systems for fired heaters.

3. General

This Procedure uses both English and metric units to provide a better understanding of what is expected in the Basic Engineering Design Questionnaire (BEDQ). However, to simplify the text, only English units are used in the calculations and examples.

If a system design includes heat integrated fired heaters, contact the Heater Group early in order to develop an appropriate plan.

4. Definitions

4.1 Net Heating Value (NHV)

NHV is also known as lower heating value (LHV). This value reflects the heat of combustion less the latent heat of vaporization for water formed during combustion.

Units: liquids - Btu/lb (kcal/kg)

gases - Btu/SCF (kcal/kg)

4.2 Viscosity

Viscosity is a fluids’ internal resistance to flow. In the , fuel oil viscosities are commonly measured using the Saybolt Universal Viscometer. The results are reported as Saybolt Seconds Universal (SSU). The metric system uses kinematic viscosity expressed in centistokes (cS; sometimes cSt), based on centipoise viscosity divided by density. Saybolt and Kinematic viscosity equivalents are located in ASTM Procedure D2161.

4.3 Headers

a. Circulating Fuel Oil Header

The circulating fuel oil heater, also known as supply header, refinery fuel oil header, main supply header, etc. The design objective is to provide fuel oil at the burner at a viscosity that will allow proper fuel atomization. The Contractor is responsible for this header design. Inflection Point Engineering does not provide line sizes or heat tracing objective temperatures on Piping & Instrument Diagrams (P&ID). When Inflection Point Engineering is responsible for the Fuel System Offsites design, contact the appropriate Process Specialist.

b. Fuel Oil Return Header

The Contractor is responsible for this return header, as described in Section 4.3.d. The individual heater fuel oil return lines are shown on the P&ID.

c. Refinery Fuel Gas Header

Also known as the main supply header, F.G. header, etc. The Contractor is responsible for sizing this header. In this procedure the term (Ph) is applied to the "header normal operating pressure" from the BEDQ (psig; kg/cm²g).

d. Header

The two gas headers shown on the P&IDs and identified as "headers" are also known as the burner gas distribution header and the pilot gas distribution header. These headers are located close to the heater after all controls and before the burners or pilots. Inflection Point Engineering sizes these headers. In this procedure, the terms (Pb) and (Pp) apply to the "burner pressure" and "pilot pressure," which are measured just downstream of these headers. The most commonly encountered of these pressure values are:

Burner pressure (Pb): liquids - 75-95 psig

gases - 20 psig

Pilot pressure (Pp): gases - 12 psig (5 psig: for special cases)

4.4 Heater Duty

There are two main types of duty referred to in the heater specification, heat absorbed and heat released (a.k.a. fired duty). The absorbed duties are listed in the Process Design Conditions section (Sheet 2) of the 201 and 202 specification. The heat release duties are listed in the Burner Data section (Sheet 3). The ratio of the absorbed to the heat release duties on a percent basis is the efficiency. The absorbed duties are reported by the Design Engineer on the Heater Summary Sheet, and the heat release duties are calculated by the Heater Specialist (see below). All duties are specified in MMBtu/hr (MMkcal/hr).

a. Normal heat release – defined as the absorbed duty divided by the calculated efficiency for the design case for the fired heater.

b. Design heat release – defined as the normal heat release with a margin added, which is contingent upon the number of burners.

The Heater Specialist uses the absorbed duty to design the heater, and the heat release duty when specifying the burners. The Design Engineer uses the design heat release duty in the fuel system design.

4.5 Gross Heating Value (GHV)

GHV is also known as higher heating value (HHV). This value reflects the heat of combustion, including latent heat of vaporization for water formed during combustion. GHV, as presented in this procedure, is not used in fuel system design, but is commonly used for sales of fuels. Read curves and tables carefully.

5. Basis and Review

Inflection Point Engineering's design practice is to specify a generic fuel system for the fired heater. This system includes the fuel treatment package, fuel piping, instrumentation and burners. The entire system is based around using Callidus burners with a fuel oil header normal pressure of 145 psig (min) and a fuel gas header normal pressure of 33 psig (min). For fuel systems utilizing steam as the atomization media, the steam shall be provided at 30 psig above the fuel oil pressure at the burner. If the Customer can meet these requirements, the Inflection Point Engineering fuel system can be used as is. If the Customer cannot, or is not willing to, meet our requirements, it becomes the duty of the Contractor to modify the fuel system.

The fuel treatment system has been newly defined to address the newest low NOx technology burners. To further reduce NOx emissions, burners are being designed with extremely small fuel ports, which are especially prone to plugging. The objective of the fuel gas treatment package is to keep burner maintenance problems to a minimum. The entire package is comprised of, in order, a knockout drum, basket strainer, fuel gas coalescer and fuel gas superheater. The knockout drum prevents large slugs of liquid from loading the coalescer, while the basket strainer reduces the dirt loading during times of coalescer maintenance. When the fuel gas superheater is specified, the fuel line downstream of the heater will be insulated. If the fuel gas superheater is not specified, the fuel line shall be traced.

The BEDQ is a primary source of information for fuel system designs. The Utility Information section contains the information discussed herein. The figures and table referred to in this procedure will help the Design Engineer/Project Manager review the correctness and completeness of BEDQ information supplied by the Customer. Conduct this review early in a project so Inflection Point Engineering can contact the Customer for clarification and avoid costly delays.

5.1 Fuel Oil NHV

Use Figure 1 – Liquid Heat of Combustion, taken from the API Technical Data Books, to review the approximate correctness of the net heating value of the fuel oil as supplied by the Customer in the BEDQ.

Contact the Heater Group if heating values need to be derived.

5.2 Fuel Gas NHV

Use or to review the approximate correctness of the net heating value of the fuel gas as supplied by the Customer in the BEDQ. Note that Customers have, on occasion, inadvertently listed gross heating values instead of NHV.

Contact the Heater Group if heating values need to be derived.

5.3 Fuel Oil Viscosity

a. Viscosity - Temperature Charts

As requested in the BEDQ, fuel oil viscosities are required at two temperatures. Use Tool to obtain estimated viscosities at other temperatures. One viscosity and temperature point can be used.

If a need to check basic viscosity data arises, reference the Physical Properties of Fluids Section of the TEMA Standards.

b. Fuel Temperature at Burner (Tb)

Set the fuel oil temperature at the burner to provide a 100 SSU (20 cS) viscosity oil.

c. Circulating Fuel Oil Header Temperature (Th)

Set the header temperature 10F (5C) above the burner temperature. Inflection Point Engineering estimates that the fuel oil temperature drops 10F (5C) in the individual heater supply lines when including heat losses from flanges and flexible hoses. The BEDQ states that the fuel oil viscosity at the burner temperature (Tb) shall not exceed 100 SSU (20 cS).

Using the viscosity calculator tool indicated in 5.3a, confirm the supply header normal operating temperature (Th) is high enough to meet the criteria for the viscosity at the burner. Notify the Customer if this criterion is not met in the BEDQ information.

(Th) = (Tb) + 10F for viscosity < 100 SSU

d. Fuel Oil Return Header Objective Temperature

This return header is normally a non-flowing line. Set the heat tracing objective temperature to maintain a viscosity less than 5000 SSU (1100 cS). If the objective temperature is greater than 150°F, the fuel oil return line shall be in continuous use.

5.4 Circulating Fuel Oil Header Pressure (Ph)

The minimum value for the normal operating pressure, as provided by the Customer in the BEDQ, must be at least 145 psig (10.2 kg/cm²g) for the main supply. The pressure in this header is typically a controlled value. Notify the Customer if this criterion is not met.

The fuel oil pressure at the circulating supply header is the sum of the operating pressure at the burner and control valve, plus line pressure drops. Typical hydraulics show 75 – 95 psig as normal burner pressure (Pb) and a 5 psi line drop from the header to the burner. A note on the P&ID limits the length of the individual heater supply line to 150 feet (45 meters).

The pressure in the fuel oil return header should be as low as possible and still return the oil to its source. If the header pressure is too high, it might limit operation of the oil guns at turndown conditions. The return header pressure should be low enough that 100% of the fuel oil supply can be flowing in the return line.

5.5 Atomizing Steam Header Pressure (Ps)

To provide good operating flexibility, the preferred battery limits supply pressure for atomizing steam is 140 psig (10 kg/cm²g). A steam system which provides a minimum value of the header pressure (Ps) of 125 psig (8.8 kg/cm²g) at the BEDQ minimum steam pressure level must be available.

This is the steam header pressure upstream of the atomizing steam PDC control valve. Set this pressure as follows:

Burner (Pb)	-	75	psig	(1)
Steam (Pa) = (Pb) + 30	-	30		(2)
CV ( P)	-	30
Line	-	5
Header (Ps)	-	140	psig

(1) Inflection Point Engineering designs are normally based on Callidus burners, which are designed for an oil pressure between 75 - 95 psig normal and 100 psig maximum oil pressure at the burner.

(2) Always set the atomizing steam pressure (Pa) at the burner to be 30 psig above the burner oil pressure (Pb).

Contact the Heater Group if the Customer specifies a fluid other than steam as the atomizing medium.

6. Determining the Flow Rate

Determine certain flow rates in order to establish line sizes and develop a heater firing P&ID. Base the fuel oil, fuel gas, pilot gas, and atomizing steam flow rates on design heat release duties. When a project with more than one process design case requires multiple heaters/interheaters, the Design Engineer must identify the design duty for each individual heater. Different cases might govern different heaters. Following are the guidelines for determining various flow rates:

6.1 Fuel Fired Calculations

Two pieces of information are needed to determine the flow rate of fuel oil and/or fuel gas fired (consumed): fuel oil and/or fuel gas NHV and design heat release duty.

Even though the heater specification may not be available when the line sizing calculations are done, the Heater Specialist should be able to provide the normal heat release. However, if this duty cannot be provided, the normal heat release can be calculated using an approximate efficiency (see below), and the design heat release can be estimated by adding an approximated 20% margin onto the normal heat release. To estimate the efficiency used in calculating the normal heat release, use , Efficiency vs. Inlet Temperature for natural draft heaters. This figure is based upon the excess air values, which may turn out to be different than the numbers in the project specification. However, a reduction in excess air by 5 percentage points causes an approximate 1 percent increase in efficiency. In line sizing calculations, this increase is insignificant.

(Burner) Normal Heat Release =

(Heater) Design Absorbed Duty (from summary sheet)/Efficiency (Btu/hr)

Fuel Fired =

(Burner) Normal Heat Release *1.20/NHV (lb/hr or SCF/hr)

The flow rates of fuel gas and/or fuel oil form the basis for line sizing. Note the fuel gas flow rate used for Project Specification 965, "Fuel Gas Preparation System" (or Project Specification 913, "Coalescers" should a customized project specification be required) is not calculated in the same way. See Section 14.1 for this calculation.

When integrated fired heaters are part of the unit design, consult the Heater Group to clarify which efficiencies apply for fuel fired determinations. For example, when flue gas from an all radiant heater are ducted to the convection section of another heater, the efficiency for the radiant/convective heater can exceed one hundred percent. The overall system should be analyzed to determine fuel fired rates to individual firing zones.

6.2 Pilot Burner Fuel

Inflection Point Engineering normally specifies a Callidus SR-XM-2 pilot burner (or equal). This burner is capable of acting at both high capacity (12 psig) and at low capacity (6 psig). The heater project specification also lists the actual, or estimated, number of burners. There is one pilot burner for each main burner.

Obtain pilot burner heat releases from Table 1. Determine the header size and NHV from this heat release. Taking into account the number of burners, use the following table, which makes some simplifying assumptions, to determine an approximate pilot gas burner fuel rate.

Pilot Burner Fuel

NHV (Btu/ft³)	lb/hr/burner
< 600	1.5 - 3.2
600 - 1500	3.3 - 5.5
> 1500	5.6 - 8.2

Use the following table to determine if a pilot gas distribution header line size break is being approached.

Pilot Burner Distribution Headers

Header Size, Inches*	1	1½	2
Max. Pilot Burners		-
SR-XM-2 (12 psig)	14	40	80
SR-XM-2 (6 psig)	13	38	77

*Schedule 80 pipe size

Typically the pilot gas distribution header size is set at 1 inch. Check the header line size when there are 15 or more burners per firing zone:

Criteria: (P/100') max = (0.05) (Pp)

Where (Pp) = pilot pressure (12 or 6 psig)

6.3 Atomizing Steam

The recommended atomizing steam flow rate is based on the Callidus oil burner that Inflection Point Engineering normally specifies.

Criteria: Flow Rate = 0.3 lb steam/lb oil

(P/100') max = 2.0 psi

7. Fuel Gas Line Sizing

Use the fuel fired rate, as described in Section 7.1, to determine the line size. The criteria for selecting line sizes are detailed as follows.

7.1 Line Sizing before Control Valve

a. Pressure drop shall be lessor of:

(P/100') max = (0.03) (Ph) or (1.5 psi/100')

b. Where (Ph) is 50 psig, (P/100') target value is (0.03) (50) = 1.5 psi

c. Design for an equivalent length of 100 feet

7.2 Line Sizing after Control Valve

a. Pressure drop shall be lessor of:

(P/100') max = (0.04) (Pb) or (1.0 psi/100')

b. Where (Ph) is 30 psig or greater, (Pb) is set at 17 psig and (P/100') target value is (0.04) (17) = 0.68 psi

c. Design for an equivalent length is 200 feet

7.3 Burner Distribution Header Size

The header size shall be the same as the line after the control valve.

7.4 Special Cases

a. (Ph) is less than 30 psig, but greater than 15 psig. Criteria:

Set up the hydraulic distribution of pressure drop in the following manner:

Piping P to CV = (0.023) (Ph)

CV P = (0.330) (Ph)

Piping P from CV = (0.047) (Ph)

Burner Pressure (Pb) = (0.600) (Ph)

When (Ph) is 15 psig, this gives a burner pressure of 9 psig and the control valve about 5 psig.

b. When (Ph) is less than 15 psig, the design requires the approval of both the Heater and Instrument Groups.

8. Fuel Oil Line Sizing

8.1 Heater Supply Line

Use the fuel fired rate to determine the individual heater fuel oil supply line size. This flow rate is based on the fuel oil fired with no return circulation. Note that this is in the laminar flow regime with oil properties of about 0.9 specific gravity and 100 SSU viscosity. Standard friction factors and nomographs do not apply.

Flow Rate

gpm	lb/hr	Size - Sch.
0-2	0-900	NPS 1- 80
2-14	900-6300	NPS 1½ - 80
14-40	6300-18000	NPS 2 - 80
40-120	18000-54000	NPS 3 - 40

8.2 Heater Return Line

When the fuel oil return line is used, it is designed for 2/3 of the flow in the supply line.

9. Pilot Gas Line Sizing

Always set the pilot gas line size at 3/4 inch. Section 7.3 covers header sizing.

10. Atomizing Steam Line Sizing

The following criterion sets the atomizing steam line size:

(P/100') max = 2.0 psi

11. Instrumentation

Other documentation covers instrumentation for fired heaters. Reference ". The P&I Department Heater Firing Section modules depict various control systems. Note that Instrument Engineers work with normal heat release and the corresponding fuel flow when specifying differential instruments and control valves in fuel systems. Some general information is provided below.

11.1 Heater Firing Controls

a. Fuel oil and fuel gas control valves can be on either pressure or flow control for natural draft heaters. Forced draft heaters are on flow control for fuel oil and fuel gas.

b. Low pressure and high pressure alarms are provided on both the fuel oil and fuel gas. The following are recommended settings for these alarms:

Fuel	Low	High
Oil	35 psig	100 psig
Gas	3 psig	24 psig

c. To provide minimum protection, there is a minimum burner pressure controller. The following are recommended setpoints for the minimum burner pressure controller:

Fuel Oil - 30 psig

Fuel Gas - 2 psig

11.2 Control Valve Sizing

a. Single Fuel

Use 100% of the fuel flow corresponding to the minimum heat release as the normal flow. Control valve CV is approximately equal to 2 times the normal calculated CV.

b. Dual Fuel (Combination oil and gas)

Use 100% of the fuel flow corresponding to the minimum heat release as the normal flow. Control valve CV is approximately equal to the normal calculated CV.

12. Winterizing and Heat Tracing

Although Procedure covers determination of objective temperatures, a more conservative approach is warranted for fired heater fuel gas lines. Customized P&ID’s are not normally required for the Fuel Gas Preparation System. shows the typical arrangement of equipment in the fuel gas preparation system (Described in ).

Presence of either tracing or insulation is required to be shown on Heater Firing P&ID modules. For fuel gas firing, fuel gas lines on Heater Firing P&ID modules need to be traced if no fuel gas superheater is present. If this is supplied (as is required by Project Specification 965 and Inflection Point Engineering Standard Drawing 2-102) insulation only of these lines is adequate. If heat tracing is required, the objective temperature is set at 100°F (38°C) unless there are heavies in the fuel in which case tracing objective temperature is increased as described below.

For fuel oil firing, as previously noted in Section 5.3, set the fuel oil supply and return line objective temperatures to maintain SSU viscosities of 100 and 5000 respectively. When the required fuel oil objective tracing temperature exceeds 350°F (176°C), or the winterizing temperature is less than -20°F (-29°C), the instrument and heater groups will make special recommendations.

In the exceptional circumstance where customized P&ID’s and (or) project specifications for fuel gas preparation system are required, the following guidelines apply:

The fuel gas treatment package utilizes a fuel gas superheater downstream of the fuel gas coalescer to superheat the gas and ensure no condensation, and therefore, less potential for plugging and coking on the burner tips. Ideally, the Customer will choose the entire treatment package, but if only parts will be specified, use the rules below to determine if tracing is necessary and, if so, where it should begin.

• Knockout drum only: trace lower section of drum and lines downstream, and insulate entire drum
• Knockout drum and coalescer: trace lines downstream of coalescer
• Knockout drum, coalescer, and fuel gas superheater: insulate downstream of superheater

When tracing is required, trace fuel gas lines for a 100°F (38°C) objective temperature, unless there are heavies present in the fuel gas. For heavier fuel gases, the following objective temperatures shall apply:

• For fuels with more than 30 volume percent C3’s, the bulk temperature shall be 150°F (66°C) minimum.
• For fuels with more than 30 volume percent C4’s, the bulk temperature shall be 200°F (93°C) at normal conditions and 150F minimum.
• For fuels with more than 30 volume percent C5’s and heavier, the bulk temperature shall be 250°F (120°C).

If the C5 plus content of a fuel gas seems high, check the dew point temperature at the system pressure (Ph). Usually, this situation does not occur until the C6 plus content is more than a few tenths of a percent. If this calculated dew point temperature is higher than 100°F (38C), and no fuel gas superheater is specified, then trace the fuel gas system downstream of the fuel gas knockout drum to an objective of 100F above the dew point temperature. This is likely to occur when the fuel gas is derived from hot receivers, e.g., Pacol stripper receivers at 175-185F (79-85C).

When the fuel gas knockout drum is in Inflection Point Engineering’s scope of work, and no fuel gas superheater is specified, start this tracing at the vapor outlet of the drum. For intermittent service fired heaters, such as startup heaters and direct fired air heaters, consult with the Process Specialist to determine the need for gas line tracing.

When the winterizing temperature is 32F (0C) or less, trace and insulate the fuel gas knockout drum in the bottom area (if no fuel gas superheater is specified). The bottom head and vessel shell up to the high liquid level, along with the level bridle system, have a 40F (5C) objective temperature.

13. Fuel Gas Preparation System

To meet increasingly stringent flue gas NOx emission requirements, burner vendors are offering designs that increase the number of fuel gas ports, resulting in a corresponding decrease in port diameter. The smaller gas ports (orifices) are subject to blockage from pipe debris and aerosol hydrocarbon coke formation. Thus, for current, and in anticipation of future regulatory requirements, Inflection Point Engineering specifies a fuel gas preparation system for all fuel gas fired heaters regardless of the type of gas burners. The equipment required to remove solid and liquid particles entrained in fuel gas to achieve reliable and efficient low NOx burner operation is described in Project Specification 965. The Inflection Point Engineering fuel gas preparation system consists of a liquid knockout drum followed a fuel gas coalescer (with basket strainer in bypass leg), and a fuel gas heater. Utilization of all components of the Inflection Point Engineering specified system (i.e. including coalescer and fuel gas heater) is especially critical for the reliability of ultra low NOx burners. If ultra low NOx burners are not expected to be used for the foreseeable future, the contractor may (with Customer's agreement) modify the system to more cost effectively meet the less stringent needs of anticipated burners for removal of entrained particles.

13.1 The requirements of Project Specification 965 are general and recommended for all fuel gas fired heater applications. Therefore the project specification should not normally require customization to a particular project and should to be specified in all instances of fuel gas firing. The contractor (with Owner’s agreement) may not always utilize the full fuel preparation system for reasons stated in the preceding paragraph; the BEDQ states ‘the installation of a proper fuel gas preparation system is the responsibility of the Owner’.

13.2 Inflection Point Engineering Standard Drawing 2-102 shows the typical arrangement of equipment in the fuel gas preparation system. This standard drawing is referenced in Project Specification 965 and is to be provided along with that project specification to fully describe the fuel gas preparation system. In normal circumstances this drawing replaces the requirement to provide project specific P&ID’s for the fuel gas preparation system.

13.3 The Inflection Point Engineering Schedule A design assumes a separate and complete Fuel Gas Preparation System is required for each process unit with a fired heater. During the detailed design, the Contractor may (with Customer agreement) combine the requirements for two or more process units into a single Fuel Gas Preparation System when the heaters are clustered closely together.

In certain exceptional circumstances (e.g. where this is agreed in Inflection Point Engineering scope) customized project fuel gas knockout drum and/or coalescer specifications (Project Specification “301, Vessels”) for the fuel gas knockout drum and Project Specification 913, “Fuel Gas Coalescer”) and customized project P&ID’s may be required. The sections below (14 and 15) describe this equipment and requirements for producing these specifications.

14. Fuel Gas Knockout Drums

In many instances the fuel gas knockout drum is part of Offsites and is provided by others. Inflection Point Engineering only provides fuel gas knockout drums upon the Customer’s request. In normal circumstances the specification of the fuel gas knockout drum is covered by Project Specification 965 and Inflection Point Engineering Standard Drawing 2-102 and no further (i.e. job specific) specification of this equipment is required. In exceptional circumstances (e.g. where this is agreed in Inflection Point Engineering scope) a customized project knockout drum specification with sizing may be required and the instructions in the remainder of this section apply. If this is the case, it is important to determine if individual heater knockout drums are required, or if one knockout drum can serve a group of heaters. Refer to for additional information.

14.1 Drum Sizing

To size the knockout drum, use Inflection Point Engineering Vessel Design: Program P254, along with and Procedure PSD-301-01, “Fuel Gas Knockout Drum” for additional information. Fuel gas viscosities can be obtained from Figure 16-27, in Section 16 of the GPSA Engineering Data Book.

14.2 Mesh Blankets

Provide three (3) 3 inches thick (total of 9 inches) Monel mesh blankets with a minimum diameter of 8 inches to provide enough area to avoid fouling. Use Inflection Point Engineering Vessel Design: P254 to determine the mesh blanket diameter. See " for additional information.

14.3 Vessel Specifications

is a copy of Project Specification 301, “Vessels”, which is used for fuel gas knockout drums. It was developed using the Inflection Point Engineering Vessel Design computer program for vertical vessels. See Procedure PSD-301-01, “Fuel Gas Knockout Drum” for additional information.

14.4 Piping and Instrument Drawings

is a copy of the English units version of the P&ID modules available for a Fuel Gas Knockout Drum. The specific modules available are located in Section 18, Heater Firing, in the P&I Department Modules Book.

is a reduced copy of one of the heater firing modules. This figure is provided to help identify the various headers and lines described in this Procedure.

15. Fuel Gas Coalescer

In normal circumstances the specification of the fuel gas coalescer is covered by Project Specification 965 and Inflection Point Engineering Standard Drawing 2-102 and no further (i.e. job specific) specification of this equipment is required. In exceptional circumstances (e.g. where this is agreed in Inflection Point Engineering scope), a customized project coalescer specification (Project Specification 913, “Fuel Gas Coalescer”) may be required and the instructions in the remainder of this section is applicable. The 913 Specification is a duty specification listing the basic design criteria (metallurgy, processing capability and nozzle sizes). Since fuel gas coalescers are a proprietary equipment design, the orientation is left to the vendor. See vendor examples .

More stringent flue gas emission requirements (legislated NOx limits) have driven burner vendors to increase the number of fuel gas ports, but decrease the port diameter in new burner designs. The smaller gas orifices are subject to blockage from pipe debris and aerosol hydrocarbon coke formation. In order to keep the debris and aerosol from reaching the burner, a basket strainer and fuel gas coalescer are specified. Since coalescing elements are sensitive to particulate loading, specifying a basket strainer keeps the dirt load to a minimum. Dual basket strainers keep large particles and dirt from reaching the coalescer elements, thereby limiting the pressure drop across the elements and increasing the service life.

Mesh blankets (three-zone, 9-inch thick – as used in fuel gas knock out drums) can remove liquid droplets down to 5 microns in diameter, this is at the upper range of the liquid aerosol scale. Therefore, to address the changing technology of the new low NOx burners, Inflection Point Engineering recommends specifying a fuel gas coalescer which will eliminate liquid droplets down to 0.3 microns (at a 99.98% removal efficiency). The improved fuel quality results in improved flame quality (shape), heat distribution, reliability and lower NOx levels and maintenance of burner tips for gas fired equipment.

The following material should be referenced when using Project Specification 913, “Fuel Gas Coalescer”.

15.1 Total Flow Rate

Mass and volumetric fuel gas rates for the range of fuel gases fired should be listed in the 913 specification. Rates specified should be 150% of the normal heat release (see section 6.1) whether the coalescer serves a single heater or a group of heaters. By specifying such a design margin, the cost of increased capacity is marginal, but the time period between replacement of the elements is increased. Most coalescer elements are considered hazardous waste; therefore, extending the operational life has a good payback.

The performance of fuel gas coalescers deteriorates at rates less than 10-to-1. Since the typical process unit turndown is 50%, the large design margin should not impact performance.

An optional mesh blanket has occasionally been used in services where a liquid waste stream is being sent directly to a coalescer, to protect the coalescing elements from large amounts of liquid (aerosol droplets of 5 micron and larger). In this case, the surge volume of the liquid will need to be added to Project Specification 913, “Fuel Gas Coalescer” along with a note requesting a mesh blanket. Mist Eliminators” should also be made available to the Customer/Vendor.

15.2 Variable Stream Properties

Vapor molecular weight and mole percent hydrogen are listed or generated from BEDQ fuel gas composition data. Generic vapor viscosity and liquid density values (for a C5/C6 mixture) should remain unchanged – unless more specific values can be generated.

15.3 Operating/Design Temperature and Pressure

Operating values are taken from the BEDQ Fuel Gas System Data, Section 3.6. The design pressure value should meet the mechanical design pressure listed in the BEDQ. If a Customer has failed to list the value of the mechanical design pressure, set the design pressure 25 psi above the maximum operating pressure.

The design temperature should be set equal to the mechanical design temperature listed in the BEDQ. If the design temperature is not listed, or the value listed is less than 250ºF, the design temperature should be set at 250ºF (120ºC).

15.4 Minimum Design Metal Temperature

Obtain this value from the Low Ambient Design Temperature section of the BEDQ, Section 4.2.

15.5 Minimum Surge Volume

Process upsets upstream of the fuel gas preparation system can expose the coalescer elements to liquid surges or heavy aerosol volumes. Liquid slugs or aerosol levels that exceed 740 ppmv can temporarily overwhelm the coalescer elements. This concern is minimized if a fuel gas knock out drum is included in the fuel gas preparation system.

Specify a surge volume equal to the length of 50 ID of inlet pipe, e.g. for an inlet of 6” NPS schedule 40 pipe the surge volume would equal 4.66 ft³ (50 x 5.581 in /12in/ft x 0.2006 ft² (transverse internal area)).

Calculation of minimum surge volume for CCR vent gas to fuel is a special case with unique design requirements governed by CCR operations. For further 913 specification design details, contact the CCR Technology Specialists.

15.6 Material of Construction / Corrosion Allowance

Typically, killed carbon steel up to, and stainless steel after the fuel gas heater are the materials of construction, but is subject to BEDQ Customer metallurgical requirements and metallurgical review.

The corrosion allowance is also subject to metallurgical review. A typical value is 0.188 in (5 mm) for killed carbon steel equipment.

15.7 Mesh Blanket Material

When a mesh blanket is called for in the BEDQ, it is generally a Monel construction material. A mesh blanket will protect the coalescer elements from particulate debris and aerosol droplets of 5 micron and larger.

15.8 Insulating Clips and Rings

If aerosol droplets were to develop down stream of the coalescer, the burner tips will plug. Unless a fuel gas superheater will be specified, tracing of the lines immediately downstream of the coalescer is required. Depending on ambient winter temperatures, drain port freeze protection may be required.

15.9 Connections, Nozzles, Manway Access

Cross-reference with project P&ID for consistency.

15.10 Reference to Inflection Point Engineering Standard Specifications and Drawings

Fuel gas coalescer designs are proprietary. Reference to Inflection Point Engineering Standard Specifications and Drawings place responsibility on the equipment vendor in addressing the following areas of design concern:

, Level Instrument Baffles

, Vortex Breakers

, Pressure Vessel Carbon Steel

, Mist Eliminators

Table 1 - Pilot Heat Release

Fuel Gas Specific Gravity	Net Heating Value, Btu/ft3	SR-XM-2 Pilot Heat Release Btu/h @ 6 psig	SR-XM-2 Pilot Heat Release Btu/h @ 12 psig
0.069	273	56,110	79,370
0.100	320	54,580	77,210
0.200	450	54,110	76,550
0.300	575	56,880	80,460
0.400	720	61,400	86,860
0.500	840	63,110	89,280
0.550	910	66,200	93,640
0.600	975	68,100	96,330
0.700	1125	72,720	102,880
0.800	1265	76,490	108,200
0.900	1410	80,320	113,630
1.00	1560	84,350	119,320
1.20	1850	91,190	129,000
1.50	2275	100,500	142,170
2.00	3014	115,150	162,900

Figure 1 -- Liquid Heats of Combustion

Procedure IPE-TM-200-02

Figure 1

Figure 2 -- Gas (Low Mol Wt.) Heats of Combustion

Procedure IPE-TM-200-02

Figure 2

Gas (Low M. WT.) Heats of Combustion

Figure 3 -- Gas Heats of Combustion

Procedure IPE-TM-200-02

Figure 3

Gas Heats of Combustion

Figure 4 -- Fired Heater Efficiencies

Procedure IPE-TM-200-02

Figure 4

Fired Heater Efficiencies

Figures 8, 9, 10 -- Typical Coalescers

Procedure IPE-TM-200-02

Figure 8 – Typical Vertical Coalescer

Figure 9 – Typical Horizontal Coalescer

Figure 10 – Typical Horizontal Coalescer with Backflush Capabilities