AU2001296308B2 - Integrated urea manufacturing plants and processes - Google Patents

Description

INTEGRATED UREA MANUFACTURING PLANTS AND PROCESSES 2 3 FIELD OF THE INVENTION 0 4 Syngas generators such as reformers and gasifiers of hydrocarbon fluids Q 5 and solid carbonaceous materials and Fischer Tropsch (FT) units primarily for 6 creating liquid hydrocarbons from syngas are combined to create an integrated c- 7 plant for providing one or more of urea, ammonia, carbon dioxide, electric power, 8 and even sulfur when dealing with sulfur-containing raw material.

9 BACKGROUND OF THE INVENTION 11 Our modern civilization cannot be sustained without burning carbonaceous 12 materials for primarily motive and electrical power within the foreseeable future.

13 The carbon dioxide (CO2) generated by such burning may be contributing to the 14 gradual increase of the planet's temperature since 1900. This is occurring because CO2 permits the sun's energy to pass through the atmosphere but traps 16 the longer wavelength energy radiated by the earth into the atmosphere.

17 The integrated plants and processes of this invention can help reduce the 18 amount of CO2 currently vented into the air through the production of the various 19 products later discussed in the description of the manufacturing plant flow diagrams. Further, the plants of this invention produce substantial energy 21 savings by balancing exothermic and endothermic reactors as discussed below.

22 A variety of syngas generators are known, reformers, autothermal 23 reactors, and gasifiers. Thus, U.S. Pat. 5,611,947 to J. S. Vavruska, U.S. Pat.

1 1 5,993,761 to Piotr and Albin Czernichowski and U.S. Patent 6,153,852 to A. F.

2 Blutke et al. all teach plasma reformers useful in constructing the integrated 3 facilities used in the process of this invention. Likewise, Charles B. Benham et 0 4 al., U.S. Patent 5,621,155, utilize reformers to provide feed streams to Fischer O 5 Tropsch reactors utilizing iron-based catalysts. U.S. Pat. No. 6,306,917 to Mark 6 S. Bohn et al. teaches that hydrocarbons and electric power can be manufactured c- 7 at a plant using the Fischer-Tropsch (FT) reactors. It also suggests that urea can 8 be produced but no suggestion is given as to how to manufacture the urea or the 9 practicality of such a course of action.

The above references to and descriptions of prior proposals or products 11 are not intended to be, and are not to be construed as, statements or admissions 12 of common general knowledge in the art in Australia.

13 The mentioned references deal with economic niches where tax 14 incentives, regulatory penalties and other incentives must combine with other factors to make the processes commercial. A continuing increase in world 16 temperatures or a more firm tie-in between the CO 2 in the atmosphere and 17 increasing world climate temperatures could quickly result in such incentives.

18 The plants can be of particular utility when sited at remote locations where there 19 is a large surplus of natural gas, petroleum, coal or other carbonaceous materials which are presently unrecoverable because of transportation costs, etc.

21 Increasing regulatory demands have limited, and, in some instances 22 extinguished, the petroleum producers' and refiners' ability to flare waste gases.

23 Further, there are often limitations on the amounts and kinds of other wastes that 2 ct 1 can be disposed of locally without harm to the environment, at an offshore 2 crude oil producing platform. The multi-product plants of this invention provide a 3 mechanism for packaging the various unit processes required for the utilization of 00 4 this invention in a manner that the resulting plants can be utilized to supply Q 5 electricity for a platform, eliminate the need for flares, convert the waste gases 6 and liquids normally flared into liquid hydrocarbons, ammonia and/or urea while c 7 substantially eliminating local CO2 emissions. Solid commercial products can 8 also be produced for agriculture, sulfur and urea prills. Such self-contained 9 plants provide trade-offs; for offshore petroleum and/or natural gas platforms, which can improve their economic life span. This is particularly true where the 11 deposits being recovered are sour or include some C02 production.

12 The unit processes of this invention may be each individually well known 13 and the economics of the processes may have been commercially proven.

14 However, the joining of these unit processes as taught herein provides a utility for environmental and other purposes that has heretofore been unforeseen.

16 17 SUMMARY OF THE INVENTION WO 03/027062 PCT/US01/30017 Ammonia, carbon dioxide, hydrocarbons, electric power and urea are producible as products by the reaction of oxygen, water and a carbon source in a syngas generator to produce a syngas, utilizing a water gas shift mechanism to provide C02, reacting the syngas in an FT reactor to produce FT hydrocarbons and hydrogen, reacting the hydrogen with nitrogen from the air separation oxygen plant to form ammonia, then reacting the CO2 and ammonia to form urea.

Electric power can be produced by combustion of hydrogen in a gas turbine used to drive an electricity generator and/or utilizing steam formed during syngas production to drive a steam turbine which, in turn, drives an electricity generator.

Sulfur and various heavy metals can be recovered when sulfur or metalcontaining carbon sources are utilized. As noted, a number of the compounds, an element and electric power produced in the manufacture of ammonia can be "packaged" for commercial sale.

BRIEF DESCRIPTION OF THE FIGURES The Figures illustrate the favorable economics and ease of interaction which can be obtained through a combination of several well known unit processes and for manufacturing a variety of materials, all of which can be provided in amounts suitable for commercial sales if suitable raw materials are available.

Figure 1 depicts a syngas producing unit and an FT unit combined to provide liquid hydrocarbons and electric power.

ct 1 Figure 2a utilizes the basic plan of Figure 1 and delineates the minimal 2 equipment and indicates the valving and other plumbing changes needed to 3 convert the unit of Figure 1 into an ammonia manufacturing plant utilizing 00 4 hydrocarbon gases from a substantially solid carbonaceous feed such as coal and petroleum refining residues.

S6 Figure 2b depicts the added equipment needed to convert the ammonia c 7 produced in the plant of Figure 2a into a urea plant.

8 Figure 3a and 3b teach an alternate exemplary plant layout for 9 manufacturing urea utilizing natural gas as the syngas feedstock.

11 DETAILED DESCRIPTION OF THE DRAWINGS 12 In the coal gasification/FT/power plant of Figure 1, crushed coal, water 13 (H 2 preferably as steam, and oxygen (02) are introduced into the syngas 14 generator 11 through piping 12, 13 and 14, respectively. The oxygen is preferably from a cryogenic air separation unit 15. However, a pressure swing 16 absorption unit can also be utilized. Either can provide nitrogen (N 2 for an 17 ammonia (NH3) plant (not shown). The hot gases are exhausted from the 18 syngas generator 11 at temperatures of 2400 0 F to 2700 OF and are cooled in one 19 or more water-cooled quench units 16 to remove slag and other minerals. The cooled syngas and soluble impurities are piped into a heat recovery steam 21 generator (HRSG) 17 which is used to heat the feed water (FW) to steam of a 22 desired temperature, 230 0 F to 600 0 F, and provide steam to power steam 23 turbine 18.

1 The syngas is piped to the acid gas removal unit (AGR) 19 to remove bulk 2 sulfur from the syngas generator 11 output. The resulting gas is then passed 3 through sulfur removal unit (SRU) 20 to remove trace quantities of sulfur.

0 4 Preferably, the SRU 20 uses a zinc oxide-based catalyst and is run at .O 5 temperatures of 600 0 F to 725 0 F. with a linear velocity of 4-10 ft/sec.

6 To the extent needed, the gaseous treated stream from the SRU 20 is then C 7 piped to the FT reactor and product separation unit 21 to obtain the liquid FT 8 hydrocarbon products. The FT reactor and product separator 21 tail gas is piped 9 to remove carbon dioxide via CO 2 removal unit 22. A second portion of the desulfurized syngas is piped to a water gas shift reactor 23, preferably designed 11 for use with a high temperature iron/chrome catalyst. The tail gas stream from 12 the FT reactor and product separation unit 21 is combined with the output of the 13 shift reactor 23 and passed through CO 2 removal unit(s) 22. Combustible 14 components from the CO 2 removal unit(s) 22 are fed to the gas turbine 24 which is used to drive a coupled electricity generator 25. Likewise, the steam turbine 18 16 can be used to drive the electrical generator(s) 25. The stack gases of the gas 17 turbine 24 are returned to heat recovery steam generator (HRSG) 17.

18 The CO 2 absorbed in the CO2 removal unit 22 is desorbed in the CO2 19 stripper unit 26 and compressed by CO 2 compressor(s) 27 for tank or other storage, preferably at pressures above 135 atm or recycled as needed.

21 In Figure 2a, the equipment differs from that of Figure 1 only to the extent 22 that the non-CO 2 output of the CO2 removal unit 22 is passed through a hydrogen WO 03/027062 PCT/US01/30017

(H

2 removal unit 28 and the recovered hydrogen is piped to an ammonia converter 38 (Fig. 2b). The non- H 2 output of the H 2 removal unit (HRU) 28 is piped to the gas turbine 24 as fuel. Preferably the H 2 removal unit 28 utilizes a membrane separator. Such units are manufactured by Monsanto Company, located at St. Louis, Missouri, USA or Air Liquide located at Paris, France.

In Figure 2b, the continuation of the flow chart of Figure 2a, the CO2 from stripper unit 26 (Fig. 2a) is compressed by CO2 compressor 27 and introduced into urea synthesizer 29 which operates at 330 0 F to 375 0 F and 2000 to 3000 psig. The urea synthesized in the urea synthesizer 29 is pumped to the urea purification unit 31 to reduce the water and other impurities. The urea is then prilled or formulated into aqueous urea or anhydrous prills for sale.

Hydrogen (H 2 from the hydrogen removal unit 28 (Fig. 2a) is passed through hydrogen compressor 32 and combined with nitrogen (N 2 from air separation unit 15 (See Fig. 1) and the mixture is passed to heater 33 to raise the temperature to about 500 0 F and introduced into methanator 34 which operates at 500 OF to 600 0 F utilizing, preferably, a 27-35% nickel oxide catalyst.

The methanator utilizes a catalyst which is delivered as nickel oxide on alumina and reduced to nickel on site for operation. A variety of suppliers market the catalyst. The methanator operates at temperatures between about 500 0 F to 550 0 F at the inlet and pressures between about 275 to about 375 psig. The methanator 34 product stream is passed through cooler 35 into ammonia/syngas compressor 36. The compressed product stream is cooled in exchanger 37 and is fed to NH3 converter 38. The resulting ammonia stream returns to the heat 7 WO 03/027062 PCT/US01/30017 exchanger 37 through line 39. The cooled effluent is further cooled in exchanger 41 and still further cooled with a cold stream from ammonia refrigeration unit 42 before passing to separator 43. The condensed ammonia from ammonia separator 43 is then passed through pump 44, piped into a urea synthesizer 29, dried for prilling or made into aqueous solutions of desired concentrations.

In Figure 3a, the liquid oxygen (02) from air separation unit 40 is passed through cryogenic pump 45, heater 46 and introduced into mixing zone 47. The natural gas is compressed to about 200 to about 500 psia in compressor 48, heated in exchanger 49 and run through a sulfur removal unit 51 to "sweeten" the raw gas and then into another heater 52 before entering the mixing zone 47. The natural gas and oxygen are converted into syngas in syngas generator 53 and cooled in exchanger 54 prior to treatment in CO 2 removal unit The absorbed CO 2 is stripped in stripper 56 prior to recycling to the urea synthesizer 29 (Fig. 3b). The syngas stream passes through heater 57 before entering FT reactor 58. The resulting products are introduced into product separator 59 to provide a liquid hydrocarbon stream with pentane or greater fractions, a stream of aqueous oxygenated hydrocarbons which is pumped from about 200 to about 500 psia by pump 60, and reheated in heat exchangers 61 and 52 prior to entering mixing zone 47. A tail gas stream also flows to mixing zone 47 via compressor 62 while the CO 2 is sent to a CO 2 compressor 63 (Fig.

3b). The flow diagram of Figure 3b shows CO 2 from the CO 2 stripper 56 passing through compressor 63 into urea synthesizer 64 and thence through a urea purification unit 65. The FT tail gas stream then passes a pressure swing 8 WO 03/027062 PCT/US01/30017 absorber 66 to remove H 2 A hydrogen-lean fraction is used as fuel while the remainder is mixed with nitrogen (N 2 from air separation unit 40, piped to heater 67 and thence to methanator 68 which removes the remaining traces of carbon oxides. The product stream from the methanator is piped into cooler 69 and then into ammonia syngas compressor 71. The compressor 71 product is cooled in exchanger 72 and introduced into ammonia converter 73. The ammonia from the converter 73 is fed to the exchanger 72, cooled in exchanger 74 by ammonia refrigeration unit 75. The ammonia stream from exchanger 74 passes through ammonia separator 76. A portion of the effluent from separator 76 is recycled to the ammonia syngas compressor 71 and the remainder is used as fuel. The purified ammonia is passed through pump 77 and mixed with compressed CO 2 before introduction to urea synthesizer 64. The urea produced is then passed through purifier 65 and readied for use or sale.

EXAMPLES

Example 1. Coal Gasification to FT Liquids. Electrical Power and COQ Example 1 is a computer simulation based on the flow sheet of Figure 1.

5500 tpd Pittsburgh #8 coal is gasified with 3328 tpd water and 5156 tpd oxygen.

The coal is 74.16% carbon. After quenching and cleaning, a portion of the syngas is sent to an FT reactor. The remainder of the syngas is shifted to convert as much of the CO to CO 2 as is possible. This shifted stream is combined with the FT reactor tail gas. CO 2 is removed from the combined WO 03/027062 PCT/US01/30017 stream and compressed for commercial usage or sequestration. The C0 2 -free gas is sent to the gas turbine to produce power.

The flow sheet takes advantage of the water-gas shift activity of an ironbased FT catalyst in converting much of the carbon in the feed coal to C02. This catalyst is discussed in U.S. Patent 5,504,118 issued to Charles B. Benham et al.

A computer simulation utilizing the equipment of this flow sheet of 5500 ton per day of coal produces 6000 barrels per day of FT liquids, 400 MW net electrical power, and 10515 ton per day of sequesterable C02. Only 9% of the feed carbon is in the stack gas.

Example 2. Coal Gasification to FT Liquids Electrical Power and Urea.

Example 2 is based on the flow sheet of Figures 2a and 2b. This flow sheet builds on the flow sheet of Example 1 by reacting the sequestered C02 with ammonia to produce urea. To make the required ammonia, nitrogen from the air separation unit is reacted with hydrogen removed from the gas stream prior to power generation. This demonstrates the synergies possible with the iron-based FT catalyst.

Using these two flow sheets, a computer simulation based on 5500 ton per day coal produces 6000 barrels per day FT liquids, 223 MW net electrical power and 4230 ton per day urea. Carbon in the stack gas is the same as in Example 1. The difference is that the sequestered C02 has been used to produce urea.

Example 3. Natural Gas to FT Liquids and Urea.

This example is based on figures 3a and 3b and the use of a sour natural gas. The natural gas is reformed with oxygen in an autothermal reformer. After WO 03/027062 PCT/US01/30017 cooling the syngas, CO 2 is removed and sent to the urea plant. The syngas is then sent to an FT reactor. Most of the FT tail gas is recycled to the autothermal reactor. The rest is used in the ammonia plant. Ammonia and CO 2 are removed from the syngas and piped to the urea plant.

In this flow sheet, a computer simulation shows that 100 MMSCFD natural gas produces 10,170 barrels per day FT liquids and 275 ton per day urea. Note that virtually all of the feed carbon ends up in the FT liquids and the urea.

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

GENERAL TEACHING OF THE INVENTION The obvious benefits of utilizing the unit operations and processes of this invention include: 1. With respect to Figures 1, 2a and 2b, there is an unexpected benefit from shifting the use of the coal gasifier operation to convert the usually desired CO to CO 2 production. It enables the heat values of the syngas to simultaneously produce electrical power and sequester CO 2 The use of ironbased FT catalysts to form CO 2 from CO allows some of the feed carbon to be sequestered as CO 2 When the sequestered CO 2 is reacted with hydrogen recovered from the syngas production, the FT tail gas and nitrogen from the air 11 WO 03/027062 PCT/US01/30017 separation unit, a synergistic benefit is obtained via the production of urea.

Further, when C0 2 from a natural gas feed, H 2 obtained from the FT tail gas and the nitrogen obtained from the air separation unit are reacted as shown, urea can be produced rather than having to vent the C02 to the atmosphere.

Feedstocks include both natural gas and low value industrial materials, coal and refinery bottoms having a hydrogen to carbon atom ratio of about 1. Feedstocks can, however, have higher ratios, natural gas with a ratio approaching 4:1. Many of these materials will include contaminants which must be removed, sulfur, arsenic and silicaceous materials which are removed during the course of the syngas manufacturing steps as slag or sulfur compounds.

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

For the purposes of this invention, iron-based FT catalysts are preferred because they produce C0 2 via their water gas shift activity. In general, the reactors, materials of construction and processes are well known to those skilled in the refining and Fischer Tropsch utilizing industries. The assembly of the reactors taught form the basis of the claimed chemical processing units sequenced in the invention. The sequenced chemical processes, catalysts, temperatures, concentrations and other stated parameters form the basis of the chemical process claims. It is to be understood that the order of the chemical processing units and the process steps and conditions described in Figures and 12 ct 1 the discussion thereof can be varied and the variations are intended to fall within 2 the claims as taught in the description and Figures.

3 When used in this specification and claims, the terms "comprises" and oo 4 "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the 6 presence of other features, steps or components.

7 8 9 11 12 13 14 16 17 18 19 21 22 23 13

Claims (5)

1. 7. The process of Claim 1 wherein at least a portion of the hydrogen from the 11 Fischer-Tropsch reactor is recovered and packaged for commercial sale. 12 8. The process of Claim 1 wherein at least a portion of the carbon dioxide is 13 recovered from the carbon dioxide stripper and packaged for commercial sale. 14 9. A process for manufacturing aliphatic hydrocarbons and urea from carbonaceous materials comprising: 16 a) reacting a carbonaceous material with steam and oxygen from an 17 air separation unit in a syngas generator to produce a mixture of gases containing 18 hydrogen, carbon monoxide and carbon dioxide; 19 b) reacting the mixture of gases in a Fischer-Tropsch reactor unit containing at least one iron-based catalyst for the formation of aliphatic 21 hydrocarbons and for the formation of carbon dioxide via the water gas shift 22 reaction; 23 c) product ga, d) e) f) separation form metha separating the aliphatic hydrocarbons from the Fischer-Tropsch ses; separating carbon dioxide from the product gases; separating hydrogen from the product gases; reacting the separated hydrogen and nitrogen from the air unit with the residual Fischer-Tropsch gases in a methanator unit to ne; g) reacting the methanator off gases in an ammonia converter; h) separating ammonia from the ammonia converter off gases; and i) reacting separated carbon dioxide with the separated ammonia in a urea synthesizer and recovering urea. The process of Claim 9 wherein the Fischer-Tropsch reactor includes an iron-based catalyst and the syngas generator operates at about 2400 0 F to about 2700 0 F.
2. 11. The process of Claim 9 wherein the catalyst used in the Fischer-Tropsch catalyst is a precipitated unsupported iron catalyst.
3. 12. The process of Claim 10 wherein the catalyst is promoted with potassium and copper.
4. 13. The process of Claim 9 wherein carbonaceous material contains sulfur and the sulfur is removed from the natural gas prior to reaction in the syngas generator. t 1 14. The process comprising separating oxygen from nitrogen from the air in an 2 air separation unit, introducing a carbonaceous raw material, water and oxygen 3 from the air separation unit into a syngas generator under syngas forming 4 operating conditions, introducing a portion of the syngas into a Fischer Tropsch 5 reactor containing an iron-based catalyst and forming primarily aliphatic 6 hydrocarbons and carbon dioxide; separating the liquid hydrocarbons from the c- 7 carbon dioxide and unconverted carbon monoxide and hydrogen in the Fischer 8 Tropsch tail gases; introducing a portion of the syngas along with water and the 9 Fischer Tropsch tail gases into a water-gas-shift reactor to product primarily hydrogen and carbon dioxide; scrubbing the carbon dioxide from the shift reactor 11 effluent and collecting it for sale or sequestration; burning the gases rich in 12 hydrogen from the CO 2 scrubber in a gas turbine combustor of a combined cycle 13 plant to drive a generator mechanically coupled to the gas turbine during the 14 production of electricity.
5. 15. The process of 14 wherein the catalyst used in the Fischer Tropsch reactor 16 is unsupported precipitated iron. 17 16. The process of Claim 15 wherein the Fischer Tropsch catalyst is promoted 18 with potassium and copper. 19 17. The process of Claim 15 wherein the weight ratio of potassium to iron in the catalyst is between 0.007 and 0.010. 21 18. The process of Claim 15 wherein the weight ratio of copper to iron in the 22 catalyst is between 0.005 and 0.015. 23 17