Section 10 — Material Requirements

Catalytic Hydrodesulphurizer

IPE Engineering Practice IPE-EP-10-1-4

Document number: IPE-EP-10-1-4 · Section: 10 — Material Requirements

SCOPE

• This Practice presents recommendations for the selection and use of materials for catalytic hydrodesulfurization (CHD) units.
• This Practice is for guidance purposes and deviation per EP 1–1–3 is not required.
• An asterisk (*) indicates that a decision by the Owner or Owner’s Engineer is required, or that additional information is to be furnished by the Purchaser.

2.0 REFERENCE

The latest edition of the following standards and publications are referred to herein.

STANDARDS AND PUBLICATIONS

DEFINITIONS

• Aggressive Environmental Service (AES) – Process services which result in material degradation such as cracking, scaling, blistering, and severe pitting and/or corrosion. Examples of such services are hydrogen service, wet hydrogen sulfide, cyanides, caustic, amine, and hydrofluoric acid. AES process fluids are defined in EP 10–2–1.
• Equipment – Each pump, compressor, product accumulator vessel, pressure relief device, valve, sampling connection system, open–ended valve or line, flange or other connector in VOC service, or devices or systems required by this Practice.
• Owner – Refining Company.
• Owner’s Engineer – A Refining Company appointed engineer.

GENERAL

• This Practice is to be used for the Owner’s projects when specifying construction materials for Catalytic Hydrodesulfurizer (CHD) units.

• The purpose of the CHD units is to remove sulfur from distillate stocks by hydrogen contact over a suitable catalyst. The feed may be kerosene, fuel oil, diesel, gas oil or a wider cut containing lighter or heavier fractions, or both.
• In a typical CHD unit, see Figure 1, the charge is deaerated, heated, mixed with hydrogen and passed over a pelletized catalyst in a reactor under pressure. In some designs, the hydrogen stream is preheated prior to mixing with the charge. The reactor effluent is cooled and the liquid product separated from the unreacted hydrogen and hydrogen sulfide in the high– and low– temperature flash drums. Normally, the hydrogen–rich gas is recycled after amine scrubbing while the liquid product flows to the stripper. In the stripping column, the liquid is stripped of dissolved hydrogen sulfide and light hydrocarbons. Stripper bottoms are the desulfurized product; the overhead gas is used for fuel. In Figure 1, the components drawn in solid lines are essential to the process. Components drawn in dashed lines are optional items that may be included in the design.

MAJOR MATERIALS AND CORROSION CONSIDERATIONS

• In CHD units, equipment exposed to high–pressure hydrogen at high temperatures is protected from hydrogen attack by proper use of chromium–molybdenum steels and austenitic stainless steels.
• Hydrogen sulfide and mixtures of hydrogen and hydrogen sulfide are corrosive to carbon steel above 550°F and 500°F, respectively. Excessive corrosion and scale formation are controlled by use of chromium–molybdenum steels (H2S only) and austenitic stainless steels (H2 and H2S mixtures).
• Copper alloy tubes generally are used in water coolers and condensers. When zinc–chromate treated water is available for cooling, all–carbon–steel exchangers may be used. Air coolers utilizing carbon steel tubes provide satisfactory service, but have experienced corrosion due to ammonium chloride or ammonium hydrosulfide deposits.
• The hydrogen chloride, formed from hydrogenation of chlorine compounds, may condense as acid or as an ammonium chloride salt. The condensation of hydrogen chloride and water may occur in the lower temperature parts of the effluent system during operation, or farther upstream on shutdown. Chloride stress corrosion cracking or pitting of austenitic stainless steels and pitting or general attack on carbon steel or low–alloy steel may result. Where such conditions are anticipated and other corrosion control measures may not be completely relied upon to prevent attack, Inconel, Hastelloy C or Monel may be used for valve trim and other critical items. Monel shall not be used in sulfiding environments where temperatures exceed 450°F.
• Ammonium hydrosulfide (NH4HS) can form in high–temperature, high pressure units in which ammonia and hydrogen sulfide are present. The presence of moist NH4HS in effluent streams is especially corrosive to carbon steel tubing at velocities greater than 20 feet per second. Heat exchanger tubing fabricated from Type 321, Type 2205 and Incoloy 800 materials has been successfully used under such conditions. Selection of tubing material will depend on cooling water quality, presence of chlorides and extent of NH4HS formation.

9.0 TABLES

TABLE 1

CONSTRUCTION MATERIALS – VESSELS

Nomenclature: CS = Carbon Steel

CA = Corrosion Allowance

NOTES:

• For temperatures between 500F and 550F, consideration should be given to using CS clad with Type 410S. Suitability of cladding will depend on the corrosivity of the CHD reactor effluent stream, temperature and hydrogen partial pressure.
• Vessel to be PWHT. Hardness of welds and heat–affected zones and PWHT requirements shall be in accordance with EP 10– 2–1 and EP 10–2–3.
• Demisters consisting of Monel grids and Teflon screens may also be used.

TABLE 2

CONSTRUCTION MATERIALS–EXCHANGERS

TABLE 2 (CONTINUED) CONSTRUCTION MATERIALS – EXCHANGERS

Nomenclature: CS = Carbon Steel

CA = Corrosion Allowance NB = Naval Brass (SB171)

NOTES:

• Welds and heat–affected zones and PWHT requirements shall be in accordance with EP 10–2–1 and EP 10–2–3. All exchanger shells or headers subject to moist H2S (greater than 50 ppm H2S) shall be post weld heat treated.
• (*) If stainless steel U–tubes are used, they shall be heat treated after bending, in accordance with EP 8–1–1. Other alloys such as AL6XN may be recommended; consult the Owner’s Engineer.

(4) (*) Aggressive environments, EP 10–2–1, should be reviewed to specify other materials; consult the Owner’s Engineer.

TABLE 3

CONSTRUCTION MATERIALS–OTHER EQUIPMENT

TABLE 3 (CONTINUED) CONSTRUCTION MATERIALS – OTHER EQUIPMENT

Nomenclature: CS = Carbon Steel

CA = Corrosion Allowance SS = Stainless Steel

NOTES:

• Hardness of welds and heat–affected zones exposed to moist hydrogen sulfide (greater than 50 ppm H2S) shall be in accordance with EP 10–2–1 and EP 10–2–3.
• (*) Exact materials and corrosion allowances will be dependent on stream composition, temperature and in some cases on the type of construction. For details, consult the Owner’s Engineer.
• Piping up to 16 inches shall be seamless. Welded piping must be fusion welded.

TABLE 4

MATERIAL SPECIFICATIONS AND NDE REQUIREMENTS

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