10/2/2013. Gas CHEMICAL PLANTS AMMONIA METHANOL UTILITIES TOWN GASS SUPPLIES ENERGY INTENSIVE INDUSTRIES. Power Generation

Transcription

1 Gas Burning Feed Stock UTILITIES TOWN GASS SUPPLIES ENERGY INTENSIVE INDUSTRIES Power Generation CHEMICAL PLANTS AMMONIA METHANOL 1

2 Fundamentals of Natural Gas Processing Natural gas has been formed by the degradation of organic matter accumulated in the past millions of years. Two main mechanisms: Biogenic Thermogenic 2

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4 Water Slf Sulfur species Mercury NORM (Naturally occurring radioactive materials) Diluents Oxygen 1) Non-associated gas that occurs in conventional gas fields 2) Associated gas that occurs in conventional oil fields 3) Continuous (or unconventional) gas. 4

5 Natural gas is colorless, odorless, tasteless, shapeless, and lighter than air Crude oil gas water are directed to a central processing and treatment t t facility normally called the gas oil separation plant (GOSP). The first step in processing of the produced stream is the separation of the phases (oil, gas, and water) into separate streams. This takes place in mechanical devices known as: This takes place in mechanical devices known as: Two-phase gas oil separators when the produced stream contains no water Three-phase separators when the produced stream contains water. 5

6 The separators are used to relieve the excess pressure due to the gas associated with the produced crude and, consequently, separating it from the oil. When water exists in the produced stream, separators are also used to separate ate the free water from the oil. Once separation is done, each stream undergoes the proper processing for further field treatment Flare Reservoir GAS Gas Processing Module Gas sales or reinjection NGL sales CO 2 &/or Sulfur sales Crude Oil Separation OIL Crude Oil Treating Field Storage Oil sales WATER Produced Water Treating Water disposal or Reinjection 6

7 This module is required to meet crude oil sales specification: 1. BS&W (Basic Sediment and Water) 2. Vapor Pressure 3. Salt 4. Slf Sulfur Content t A typical crude oil produced from a field in the Middle East before and after treatment Raw crude oil has the following materials present: Water: present in two forms: emulsions (10%) and free water (30%) Salt: 50, ,000 mg/l formation water Gas: dissolved gas (600 scf/bbl crude oil) H 2 S: 1000 ppm Treated crude oils have the following final specifications: Water content: 0.3 vol% maximum Salt content: 10 lbs (as NaCl) per 1000 barrels of oil H 2 S: 70 ppm Vapor pressure: 10 psig (4 5 psi RVP) 7

8 Produced water must be treated in order to meet reinjection or disposal specification: 1. Hydrocarbons 2. Free solids 3. Dissolved solids e.g. CaCO 3, NaCl, BaSO 4, etc. Market sales of natural gas require some specifications set by the consumers regarding the maximum contents allowable for the following: 1) Acidic gases and sulfur 2) Oxygen 3) Carbon dioxide 4) Water vapor 5) Liquefiable hydrocarbons 6) Minimum thermal heating content of the gas Two common standard conditions of temperature and pressure are used: 1) Universal scientific, reported at 32 F and 760mmHg 2) Natural gas industry, reported at 60 F and 14.7 psia 8

9 Natural Gas Sales Produced Gas Stream Conditioning NGL Extraction Fuel Recompression Stabilization Product Treating NGL Sales Conditioning 1) Dehydration 2) Sweetening NGL Extraction 1) Adsorption (SCU) 2) Absorption (lean oil) 3) Condensation a)valve b)turboexpander c)refrigeration Stabilization 1) Demethanizer 2) Deethanizer Product Treating 1) Dehydration 2) Sweetening a)h 2 S, COS, CS 2 b)co 2 Removal of water is named gas dehydration. The most common processes are: 1) Absorption (highly concentrated glycol solutions) 2) Adsorption [a solid desiccant such as silicagel, alumina or molecular sieve (zeolite)]. It is used when very low (<1 ppm) effluent water content are required. 3) Condensation 4) Other - membranes, CaCl 2, etc. 9

10 Removal of H 2 S and CO 2 The most common processes are: 1) Chemical absorption amines, potassium carbonate 2) Physical absorption SELEXOL, methanol 3) Solid bed molecular sieves, iron sponge, zinc oxide 4) Other direct conversion, membrane, extractive distillation Nitrogen removal Cryogenic fractionation from methane Operating temperatures vary with pressure but can be as low as -185 C [-300 F] Mercury removal Mercury removal is done by passing the gas across a bed of sulfurimpregnated activated charcoal where the mercury reacts to form mercuric sulfide. Effluent levels of Hg should be less than1 pbb. 10

11 WHY EXTRACT NGL? 1)Meet gas sales specification requirement such as hydrocarbon dew point 2)Upgrade the market value of the products NGL products and their markets are summarized as: Ethane(C2) Petrochemical feedstock Lightest NGL with NBP of -88 C [-127 F] Recovery can be justified in those areas where a ready petrochemical market and viable transportation exist Propane (C3) Petrochemical feedstock and fuel NBP of -42 C [-44 F] 11

12 Butanes (ic4 and nc4) Petrochemical feedstock, fuel and gasoline blending ic4 is the more volatile isomer NBP of -12 C [11 F] and the most valuable. nc4 an important feedstock for the manufacturing of monolefins (ethylene, propylene) and the diolefin, butadiene. NBP -0.5 C [31 F] Natural gasoline (ic5+) Pentanes and heavier components in a gas stream primarily consist of straight and branched chain hydrocarbon Refinery feedstock, Petrochemical feedstock Commercial NGL extraction processes can be classified as follows: Absorption lean oil Adsorption short cycle unit, hydrocarbon recovery unit Condensation mechanical refrigeration, turboexpander, valve expansion 12

13 Gas and liquid contracts usually contain the following basic considerations: GAS 1) Minimum, maximum, and nominal delivery pressure 2) Maximum water content (as a water dew point at a given pressure or as a concentration) 3) Maximum condensable hydrocarbon (hydrocarbon dew point, analysis, etc.) 4) Maximum delivery temperature 5) Allowable concentration of contaminants (H 2 S, CO 2, mercaptanes) 6) Minimum heating value 7) Cleanliness (allowable solid concentration) Liquid 1) Quality of products (vapor pressure, relative or absolute density, or by standard designation such as Commercial Propane) 2) Specifications such as color, concentration of contaminants, etc. 3) Maximum water content 13

14 Heating value (heat of combustion): The amount of heat developed by the complete combustion of a material. a)the gross or higher heating value b)the net, or lower, heating value (normally referred to in Europe) Sulfur content This limitsthe the amount of sulfur compounds to prevent corrosion, toxicity and odor when the gas is burned. Typical specification for H 2 S is 4 ppm [0.25 grain/100scf] Maximum delivery temperature A maximum delivery temperature at the transfer point may be specified. It is often about 49 C [120 F]. Water content (dew point) The mass of water per unit volume of gas or the maximum allowable water dewpoint temperature at specified pressure In the U.S. 7 lb H 2 O/MMscf [110mg/m 3 ] equivalent to a water dewpoint of 32 F at 1000 psia In Europe and Canada mg/m 3 [3-4 lb/mmscf] 14

15 Hydrocarbon dewpoint Hydrocarbon dewpoint specifications vary with climate and buyer. In north America and Europe values range from -10 to 0 C [15-32 F] at any pressure. Other Nitrogen is the most important inert Its concentration is usually limited to less than 1-2%. CO 2 A maximum 2% is typical, but the CO 2 specification is often negotiable. Liquid produced by simple separation is a mixture whose composition is fixed by equilibrium. This is sometimes called a slot cut 15

16 Raw Gas Acid Gas Desulfurization Tail Gas Tail Gas Treatment Condensate and Water Removal Acid Gas Removal sulfur Offgas to Incinerator Waste water Dehydration condensate NGL Recovery Nitrogen Rj Rejection Mercury Removal Fractionation Train Gas Sales Nitrogen Rich Gas Ethane, Propane, Butanes, Pentane + 16