CN100396662C - Integrated urea production plant and process - Google Patents

Abstract

An apparatus for the production of urea from carbonaceous material, oxygen and water (preferably steam) from an air separation unit, comprises a synthesis gas generator unit, an air separation unit, a Fischer-Tropsch unit, a carbon dioxide removal unit, a hydrogen removal unit, a methanation reactor unit, an ammonia converter unit and a urea synthesizer unit. Each of the Fischer-Tropsch liquids, ammonia, hydrogen and urea may be recovered under suitable economic conditions. The electrical power can be recovered by adding a steam or gas turbine coupled to an electrical generator.

Description

Integrated urea manufacturing equipment and method

technical field

Combining a synthesis gas generator (such as a reformer and gasifier for liquid hydrocarbons and solid carbonaceous materials) with a Fischer Tropsch (FT) unit primarily for the production of liquid hydrocarbons from to provide one or more of urea, ammonia, carbon dioxide, electricity, and even sulfur when processing sulfur-containing feedstocks.

Background technique

Our modern civilization will not survive for the foreseeable future without the burning of the carbonaceous matter that provides power and electricity. Carbon dioxide (CO ₂ ) produced by said combustion may have contributed to the gradual increase in the temperature of the Earth since 1900. This condition exists because _CO2 allows solar energy to pass through the atmosphere to the Earth, but prevents the long waves emitted by the Earth from entering the atmosphere.

The integrated apparatus and method of the present invention can help reduce the amount of _CO2 currently emitted into the air by producing the various products discussed in the following description of the manufacturing plant flow diagram. In addition, by balancing the exothermic and endothermic reactors as described below, the apparatus of the present invention will provide significant energy savings.

Several types of reformers and gasifiers are known, such as reformers, autothermal reactors and gasifiers. US 5,611,947 (to J.S. Vavruska), US 5,993,761 (to Plotr and Albin Czernichowski et al.) and US 6,153,852 (to A.F. Blutke et al.) all teach plasma conversion that can be used to construct the integrated apparatus used in the process of the present invention device. Likewise, US 5,621,155 to Charles B. Benham et al utilizes a converter to provide a feed stream to a Fischer Tropsch reactor using an iron-based catalyst. US 6,306,917 (to Mark S. Bohn et al.) teaches that hydrocarbons and electricity can be produced in a plant utilizing a Fischer-Tropsch (FT) reactor. In addition, the patent application states that urea can be produced, however, there is no suggestion of how to prepare urea or the actual method of production.

The references mentioned all deal with the economic environment where incentives such as tax incentives, administrative fines etc. have to be combined with other factors in order to industrialize the method. A continued rise in global temperatures or a closer correlation between atmospheric carbon dioxide and rising global temperatures would soon lead to the described incentives. The device will be particularly useful in remote areas where there is a large surplus of natural gas, oil, coal, or other carbonaceous substances that cannot currently be recovered due to factors such as transportation costs.

Increasing regulatory requirements have limited (and in some cases suppressed) the flaring of off-gases by oil producers and refiners. In addition, there are often restrictions on the amount and type of other waste that can be locally environmentally sound disposed of (eg, on offshore oil production platforms). The multi-product facility of the present invention provides a mechanism for integrating the various unit operations required by the present invention in such a way that the facility can provide power supply to the platform, eliminating the need for combustion, which would normally be used for combustion The exhaust gases and liquids are converted into liquid hydrocarbons, ammonia and/or urea, while localized _CO2 emissions are significantly eliminated. In addition, solid products such as sulfur and urea granules for use in agriculture can be produced. For offshore oil and/or gas platforms, the trade-off offered by such autonomous devices can improve their economic lifespan. The apparatus will be particularly useful when the waste to be recovered contains sulfur or involves some carbon dioxide generation.

The unit operations of the present invention are well known, and their economic benefits have also been verified in industrial production. However, the linkage of these unit operations taught by the present invention provides utility for environmental and other purposes that were not previously anticipated.

Summary of the invention

Ammonia, carbon dioxide, hydrocarbons, electricity, and urea can be produced by reacting oxygen, water, and carbon sources in a syngas generator that produces syngas, using the water-gas shift mechanism to provide carbon dioxide, and reacting syngas to FT in the FT reactor Hydrocarbons and hydrogen, reacting hydrogen with nitrogen from an air separation oxygen generator to form ammonia, then reacting carbon dioxide and ammonia to form urea. Electricity can be generated by burning hydrogen in a gas turbine used to drive an electrical generator and/or using steam from waste heat recovery from the syngas to drive a steam turbine (which in turn drives an electrical generator). Sulfur and various heavy metals can be recovered when using carbon sources containing sulfur or metals.

Brief introduction to the drawings

The accompanying drawings illustrate the advantageous economics and ease of interaction that can be obtained by combining several well-known unit operations to prepare a variety of materials, all of which can be supplied in quantities suitable for commercial sale if suitable starting materials are available .

Figure 1 depicts the combination of a syngas production unit and an FT unit to provide liquid hydrocarbons and electricity.

Figure 2a utilizes the basic scheme of Figure 1, depicting the simplest setup and indicating the valve and other piping changes required to convert the unit of Figure 1 into an ammonia production plant utilizing essentially solid Carbonaceous feedstocks such as coal and petroleum refining residues.

Figure 2b depicts the additional equipment required to convert the ammonia produced in the plant of Figure 2a to urea.

Figures 3a and 3b teach another exemplary plant layout for the production of urea using natural gas as syngas feedstock.

Detailed description of the drawings

In the coal gasification/FT/power plant of Figure 1, pulverized coal, water (preferably steam) and oxygen ( _O2 ) are introduced into the syngas generator 11 via lines 12, 13 and 14 respectively. Preferably, the oxygen comes from cryogenic air separation unit 15. However, it is also possible to use pressure swing adsorption. Both ways can provide nitrogen ( _N2 ) for ammonia ( _NH3 ) synthesis plant (not shown). Hot gases are withdrawn from the syngas generator 11, which operates at a temperature of 2400°F to 2700°F, and cooled in one or more water-cooled quench units 16 to remove slag and other minerals. The cooled syngas and soluble impurities are sent to a heat recovery steam generator (HRSG) 17, which heats the feed water to steam at the desired temperature (e.g., 230°F to 600°F) and uses the steam to drive a steam turbine 18. The syngas is sent to acid gas removal (AGR) 19 to remove significant amounts of sulfur from the syngas generator 11 output. The resulting gas is then passed through a desulfurization unit (SRU) 20 in order to remove traces of sulfur. Preferably, the SRU20 uses a zinc oxide based catalyst and operates at a temperature of 600-725°F with a line velocity of 4-10 ft/sec.

To achieve the desired degree of treatment, the gaseous treated steam from the SRU is then sent to the FT reactor and product separation unit 21 to obtain a liquid FT hydrocarbon product. The off-gas of the FT reactor and product separator 21 is sent via a _CO2 removal unit 22 for removal of carbon dioxide. Another portion of the desulfurized syngas is sent to the water gas shift reactor 23, which is preferably designed to use a high temperature iron/chromium catalyst. The off-gas stream from the FT reactor and product separation unit 21 is mixed with the output of the shift reactor 23 and sent through the carbon dioxide removal unit 22 . The combustible components from the carbon dioxide removal unit 22 are fed to a gas turbine 24 for driving a linked electrical generator 25 . Likewise, steam turbine 18 may be used to drive generator 25 . The flue gas from the gas turbine 24 is returned to a heat recovery steam generator (HRSG) 17 .

The carbon dioxide absorbed by the carbon dioxide removal unit 22 is desorbed in the carbon dioxide stripping unit 26 and compressed by a carbon dioxide compressor 27 for tanking or other storage, preferably at a pressure above 135 atmospheres, or recycled as needed use.

In Figure 2a, the plant shown differs from Figure 1 only in that the non-carbon dioxide output of carbon dioxide removal unit 22 is routed through hydrogen ( _H2 ) removal unit 28 and the recovered hydrogen is routed to ammonia converter 38 ( Figure 2b). The hydrogen contains traces of carbon monoxide which can be used as fuel for a small methanation reactor 34 (Fig. 2b). The non-hydrogen output of hydrogen removal unit (HRU) 28 is sent to gas turbine 24 as fuel. Preferably, the hydrogen removal unit 28 uses a membrane separator. Such devices are manufactured by Monsanto Company (located in St. Louis, Missouri, USA) or Air Liquide (located in Paris, France).

Figure 2b is a continuation of the flow diagram of Figure 2a where carbon dioxide from stripper 26 (Figure 2a) is compressed by carbon dioxide compressor 27 and introduced into urea synthesizer 29 operating at 330-375°F and 2000-3000 psig middle. The urea synthesized in the urea synthesizer 29 is pumped to the urea purification unit 31 to reduce water and other impurities. The urea is then pelletized or formulated for sale as aqueous urea or anhydrous granules.

Hydrogen ( _H2 ) from hydrogen removal unit 28 (FIG. 2a) is sent through hydrogen compressor 32 and mixed with nitrogen ( _N2 ) from air separation unit 15 (see FIG. 1), and the mixture is sent to a heater 33 to raise the temperature to about 500°F and introduce carbon dioxide removal into the methanation reactor 34, which preferably operates at 500-600°F using a 27-35% nickel oxide catalyst .

The catalyst used in the methanation reactor is added in the form of nickel oxide on alumina, which is reduced in situ to a catalyst of nickel during operation. This catalyst is sold by several suppliers. The methanation reactor operates at an inlet temperature of about 500-550°F and a pressure of about 275-375 psig. The product stream from the methanation reactor 34 is sent through a cooler 35 into an ammonia/syngas compressor 36 . The compressed product stream is cooled in exchanger 37 and fed to _NH converter 38 . The resulting ammonia gas stream is returned to heat exchanger 37 via line 39 . The cooled effluent is cooled again in exchanger 41 and again with a cooling stream from ammonia refrigeration unit 42 before being sent to separator 43 . The condensed ammonia from the ammonia separator 43 is then passed through a pump 44 and pumped into the urea synthesizer 29 where it is dried for granulation or made into an aqueous solution of the desired concentration.

In FIG. 3 a , liquid oxygen (O ₂ ) from an air separation unit 40 is sent through a cryopump 45 , heater 46 and introduced into a mixing zone 47 . Natural gas is compressed to about 200-500 psia in compressor 48, heated in exchanger 49 and passed through desulfurization unit 51 to "sweeten" the feed gas and then enters another heater 52 before entering mixing zone 47 . Natural gas and oxygen are converted to synthesis gas in a synthesis gas generator 53 and cooled in an exchanger 54 before being processed in a carbon dioxide removal unit 55 .

The absorbed carbon dioxide is stripped in a stripper 56 before being recycled to the urea synthesizer 64 (Fig. 3b). The syngas stream is passed through heater 57 before entering FT reactor 58 . The resulting product is introduced into product separator 59 to provide a liquid hydrocarbon stream with pentane or a larger portion of an aqueous oxygenated hydrocarbon stream which is pumped by pump 60 at a pressure of about 47 before reheating in heat exchangers 61 and 52. The off-gas stream also flows through compressor 62 into mixing zone 47, while carbon dioxide is delivered to carbon dioxide compressor 63 (Fig. 3b). The flow diagram of FIG. 3b shows that carbon dioxide from the carbon dioxide stripper 56 enters the urea synthesizer 64 via the compressor 63 and from there through the urea purification unit 65 . The FT off-gas stream is then passed through pressure swing adsorber 66 to remove hydrogen. The hydrogen-depleted fraction is used as fuel, while the remainder is mixed with nitrogen ( _N2 ) from the air separation unit 40, sent to heater 67, and from there to methanation reactor 68 where residual traces of carbon dioxide are removed. The product stream from the methanation reactor is sent to cooler 69 and then to ammonia synthesis gas compressor 71 . The product of compressor 71 is cooled in exchanger 72 and introduced into ammonia converter 73 . Ammonia from reformer 73 is fed into exchanger 72 where it is cooled in exchanger 74 by means of ammonia refrigeration unit 75 . The ammonia gas stream from exchanger 74 is passed through ammonia separator 76 . A portion of the effluent from separator 76 is recycled to ammonia syngas compressor 71 and the remainder is used as fuel. The purified ammonia is passed through pump 77 and mixed with compressed carbon dioxide before being introduced into urea synthesizer 64 . The produced urea is then passed through a purifier 65 for use or sale.

Example

Example 1 Gasification of Coal to FT Liquids, Electricity and Carbon Dioxide

Embodiment 1 is a computer simulation based on the flowchart in FIG. 1 . 5500 t/d of Pittsburgh #8 coal was gasified using 3328 t/d of water and 5156 t/d of oxygen. The carbon content of the coal was 74.16%. After quenching and cleaning, a portion of the syngas is sent to the FT reactor. The remainder of the synthesis gas is converted to convert as much carbon monoxide to carbon dioxide as possible. This converted gas stream is mixed with the FT reactor off-gas. Carbon dioxide is removed from the mixed gas stream and compressed for industrial use or for collection. The CO2-free gas is sent to a gas turbine to generate power.

In converting most of the carbon in raw coal to carbon dioxide, this scheme exploits the water gas shifting activity of iron-based FT catalysts. This catalyst is discussed in US 5,504,118 to Charles B. Benham et al. According to a computer simulation of the flow chart facility, using 5500 t/day of coal would produce 6000 bbl/day of FT liquids, 400 MW of net electricity and 10515 t/day of captureable CO2. Only 9% of the raw carbon remains in the flue gas.

Example 2 Gasification of coal into FT liquid, electricity and urea

Example 2 is based on the flow diagrams of Figures 2a and 2b. Urea is produced by reacting collected carbon dioxide with ammonia, the scheme being based on the scheme of Example 1. To produce the required ammonia, nitrogen from the air separation unit is reacted with hydrogen removed from the gas stream prior to power generation. This demonstrates a possible synergistic effect with iron-based FT catalysts.

Using these two flowcharts, 5500 t/day of coal will produce 6000 bbl/day of FT liquid, 223 MW of net electric power and 4230 t/day of urea according to computer modeling. The carbon in the flue gas is the same as in Example 1. The difference is that the collected carbon dioxide is used to produce urea.

Example 3 Conversion of natural gas to FT liquid and urea

This example is based on Figures 3a and 3b and utilizes sour natural gas. Natural gas is reformed using oxygen in an autoheated reformer. After the syngas is cooled, the carbon dioxide is removed and sent to the urea production plant. Then, the synthesis gas is sent to the FT reactor. Most of the FT tail gas is recycled to the autoheated reactor. The remainder is used in ammonia production facilities. Ammonia and carbon dioxide are removed from the syngas and sent to the urea production plant. In this flow chart, computer modeling shows that 100MMSCFD of natural gas will produce 10,170 barrels/day of FT liquids and 275 tons/day of urea. Note that almost all feedstock carbon is converted to FT liquid and urea.

The simulation of the coal gasifier was based on the syngas composition given in Table 1 of "Syngas Production from Various Carbonaceous Feedstocks" (Texaco Gasification Process for Solid Feedstocks, Texaco Development Corporation, 1993). The simulation of the Fischer-Tropsch reactor was based on Rentech's iron-based catalyst (US 5,504,118).

General Teachings of the Invention

Obvious benefits of utilizing the unit operations and methods of the present invention include:

For Figures 1, 2a and 2b, there are unexpected benefits brought about by switching the purpose of the coal gasifier from producing carbon monoxide, which is often desired, to producing carbon dioxide. It enables the calorific value of the syngas to simultaneously generate electricity and produce carbon dioxide. Formation of carbon dioxide from carbon monoxide using an iron-based FT catalyst enables some of the raw carbon to be captured as carbon dioxide. Synergistic benefits will be gained through the production of urea when the captured CO2 is reacted with hydrogen recovered from syngas production, FT tail gas and nitrogen from the air separation unit. Additionally, as shown, when reacting carbon dioxide from the reformed natural gas feedstock, hydrogen from the FT tail gas, and nitrogen from the air separation unit, urea can be produced without venting the carbon dioxide to the atmosphere.

Feedstocks include natural gas and low-priced industrial materials such as coal and refinery bottoms with a hydrogen/carbon atomic ratio of about 1. However, the feedstock may have a higher ratio, such as natural gas in a ratio of about 4:1. Most of these materials will include impurities (such as sulfur, arsenic, and silicon-containing materials) that must be removed as slag or sulfide-containing materials during the synthesis gas production step.

The syngas produced can be adulterated with carbon dioxide and unwanted impurities such as chlorine, chlorides, and other toxic materials that must be safely removed and stored.

For the present invention iron based FT catalysts are preferred because by virtue of their water gas shifting activity they will generate carbon dioxide. In general, reactors, materials of construction and methods are well known to those skilled in the refining and Fischer Tropsch industries. The taught combination of reactors forms the basis of the ordered combination chemical processing plant claimed in the present invention. The ordered combination of chemical method, catalyst, temperature, concentration and other indicated parameters forms the basis of a chemical method claim. It should be understood that the sequence of chemical treatment devices and method steps and various conditions described in the accompanying drawings and discussions thereof can be adjusted, and said adjustments should be included in the scope of protection taught by the description and accompanying drawings of the present invention Inside.

Claims (21)

1. A method for preparing aliphatic hydrocarbons and urea from carbonaceous substances, comprising: a) reacting carbonaceous substances with steam and oxygen from an air separation unit in a synthesis gas generator to produce a gas mixture containing hydrogen, carbon monoxide and carbon dioxide; b) reacting said gas mixture via a water gas shift reaction in a Fischer-Tropsch reactor comprising at least one iron-based catalyst for the formation of aliphatic hydrocarbons and for the formation of carbon dioxide; c) separation of aliphatic hydrocarbons from Fischer-Tropsch gas products; d) separating carbon dioxide from the gaseous product in a carbon dioxide separator; e) separation of hydrogen from gaseous products; f) reacting the separated hydrogen and nitrogen from the air separation unit with the remaining Fischer-Tropsch gas in the methanation reactor unit to form methane and ammonia-containing methanation reactor off-gas; g) reacting ammonia-containing methanation reactor off-gas in an ammonia converter; h) separation of ammonia from the ammonia converter off-gas; and i) Reaction of separated carbon dioxide with separated ammonia in a urea synthesizer and recovery of urea. 2. The method according to claim 1, wherein said syngas generator is operated at a temperature of about 2400-2700°F. 3. The process according to claim 1, wherein at least one catalyst is a precipitated, unsupported iron catalyst. 4. A process according to claim 2, wherein said catalyst is promoted with potassium and copper. 5. The method according to claim 1, wherein said carbonaceous material is sour natural gas, and sulfur is removed from the natural gas prior to reaction in the syngas generator. 6. A method of producing aliphatic hydrocarbons from carbonaceous matter, comprising: a) separating oxygen from nitrogen in air in an air separation plant; b) introducing carbonaceous feedstock, water and oxygen from an air separation unit into a synthesis gas generator under operating conditions to form synthesis gas; c) introducing a portion of the synthesis gas into a Fischer-Tropsch reactor comprising at least one iron-based catalyst and forming mainly liquid aliphatic hydrocarbons, a Fischer-Tropsch reactor tail gas comprising mainly carbon dioxide and unconverted carbon monoxide and hydrogen; d) separating liquid hydrocarbons from the Fischer-Tropsch reactor tail gas; e) introducing a portion of the synthesis gas together with water into a water gas shift reactor to produce primarily hydrogen and carbon dioxide; f) passing the water gas shift reactor effluent and the Fischer-Tropsch reactor tail gas through a carbon dioxide separator; g) Combusting at least a portion of the combustible components from the carbon dioxide separator in a combustor of a gas turbine mechanically connected to an electrical generator to generate electrical power. 7. A process according to claim 6, wherein at least one iron-based catalyst is unsupported precipitated iron. 8. A process according to claim 6, wherein at least one iron-based catalyst is promoted with potassium and copper. 9. The process according to claim 1, wherein at least one catalyst is a precipitated iron catalyst promoted with copper and potassium. 10. The process according to claim 6, wherein at least one iron-based catalyst is a precipitated iron catalyst promoted with potassium and copper. 11. The method of claim 6, wherein at least a portion of the hydrogen produced by the syngas generator is combusted in a gas turbine combustor. 12. The method of claim 1, further comprising the step of combusting at least a portion of the hydrogen produced by the syngas generator in a gas turbine combustor to generate electricity. 13. The method of claim 6, wherein at least a portion of steam recovered from operation of the syngas generator and Fischer-Tropsch unit is introduced into a steam turbine to generate electricity. 14. The method of claim 1 further comprising the step of directing at least a portion of steam recovered from operation of the syngas generator and Fischer-Tropsch unit into a steam turbine to generate electrical power. 15. A process according to claim 6 which includes directing the non-carbon dioxide stream from the carbon dioxide separator to a hydrogen removal unit and recovering hydrogen therein. 16. The method according to claim 15, further comprising: h) reacting hydrogen from the hydrogen removal unit and nitrogen from the air separation unit in the methanation reactor unit to form methane and methanation reactor off-gas; i) reacting the methanation reactor tail gas in the ammonia converter; j) separating ammonia from the ammonia converter product; and k) In the urea synthesizer, the carbon dioxide separated from the carbon dioxide separator is reacted with the separated ammonia and the urea is recovered. 17. A method according to claim 16, wherein at least a portion of the ammonia from the ammonia converter is separated and compressed. 18. The method according to claim 1, wherein at least a portion of the ammonia from the ammonia converter is separated and compressed. 19. The method according to claim 6, wherein sulfur is separated from the synthesis gas by means of a desulfurization unit before being fed to the FT reactor. 20. The method according to claim 6, wherein at least a portion of the hydrogen from the Fischer-Tropsch reactor is recovered. 21. A method according to claim 1 or 6, wherein at least a portion of the carbon dioxide is recovered from the carbon dioxide separator.

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