Making fischer-tropsch liquids and power

Details Making fischer-tropsch liquids and power Making fischer-tropsch liquids and power

2001-10-23

2003-07-22

Parsa, J. (Department: 1621)

Chemistry: fischer-tropsch processes; or purification or recover

Liquid phase fischer-tropsch reaction

C518S702000, C518S703000, C208S015000, C208S016000, C060S039120, C060S039010

Reexamination Certificate

active

06596780

ABSTRACT:

BACKGROUND OF THE INVENTION
The process and advantages of gasifying hydrocarbonaceous material into synthesis gas are generally known in the industry. In high temperature gasification processes, synthesis gas is commonly produced from gaseous combustible fuels, such as natural gas and/or associated gas, and liquid and solid combustible organic fuels, such as coal, residual petroleum, wood, tar sand, shale oil, and municipal, agriculture or industrial waste. The gaseous or liquid or solid combustible organic fuels are reacted with a reactive oxygen-containing gas, such as air, enriched air, or pure oxygen, and a temperature modifier, such as steam, in a gasification reactor to obtain the synthesis gas in a oxygen deficient environment.
In the reaction zone of a gasification reactor, the contents will commonly reach temperatures in the range of about 1,700° F. (930° C.) to about 3,0000° F. (1650° C.), and more typically in the range of about 2,000° F. (1100° C.) to about 2,800° F. (1540° C.). Pressure will typically be in the range of about 1 atmosphere (100 KPa) to about 250 atmospheres (25,000 KPa), and more typically in the range of about 15 atmospheres (1500 Kpa) to about 150 atmospheres (1500 KPa).
In a typical gasification process, the synthesis gas will substantially comprise hydrogen (H
2
), carbon monoxide (CO), and lessor quantities of impurities, such as water (H
2
O), carbon dioxide (CO
2
), carbonyl sulfide (COS) and hydrogen sulfide (H
2
S). The synthesis gas is commonly treated to remove or significantly reduce the quantity of impurities, particularly H
2
S, COS, and CO
2
before being utilized in downstream processes. A number of acid gas removal systems are commercially available. Selection of acid gas removal system will depend on the degree of sulfur compounds and carbon dioxide removal required, and by the operating pressure of the acid gas removal system.
It is well known in the art that synthesis gas, also commonly referred to as syngas, can be converted to hydrocarbons in the presence of a variety of transition metal catalysts. Such metals are commonly called Fischer-Tropsch catalysts, and are known to catalyze the conversion of CO and H
2
to hydrocarbons. Common catalysts are cobalt and iron on an alumina support. Other Group VIII metals such as ruthenium and osmium are also active. Other single metals that have been investigated as catalysts include rhenium, molybdenum, and chromium. The activities of these catalysts are commonly enhanced by the addition of a variety of metals, including copper, cerium, rhenium, manganese, platinum, iridium, rhodium, molybdenum, tungsten, ruthenium or zirconium, among others. The general chemistry of the much studied Fischer-Tropsch synthesis is as follows:
n
CO+2
n
H
2
→(—CH
2
—)
n+n
H
2
O+Heat  (1)
CO+H
2
O⇄H
2
+CO
2
  (2)
The types and amounts of reaction products obtained via Fischer-Tropsch synthesis varies upon many conditions, such as reactor type, process conditions, and type of Fischer-Tropsch synthesis catalyst used. There are four main types of F-T reactors being used commercially: tubular fixed bed reactors, entrained bed reactors, fixed-fluidized bed reactors and slurry bubble column reactors. These reactors can operate in both high and low temperature Fischer Tropsch processes. There are generally two types of Fischer Tropsch synthesis catalysts, cobalt based and iron based catalysts. Typical products of the Fischer-Tropsch reaction include hydrocarbons from C
1
to C
200
or higher, with the bulk of the hydrocarbons product being in the C
1
to C
50
range with chain limiting catalyst. Most of the hydrocarbons produced are mixtures of olefins and paraffins. The Fischer-Tropsch reaction also produces varying amounts of carbon dioxide, water, and oxygenated components, including acids such as acetic acid, formic acid, propionic acid; alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, and longer chained alcohols; aldehydes, ketones and esters. Typically, these oxygenated components comprise 1 to 20 weight percent of the Fischer-Tropsch reaction product, and because of their water-soluble nature are commonly found in the wastewater product of a Fischer-Tropsch reactor. Some of the oxygenated compounds are also found in hydrocarbon phase. The amount of gaseous hydrocarbons, paraffin, olefins, CO
2
, oxygenates, liquid hydrocarbons, water, etc. depends on the type of reactor, catalyst employed and process conditions. For example, iron catalysts generally produce longer chain hydrocarbons that are more olefinic, produce less amount of water, higher amounts of oxygenates and higher amounts of CO
2
as compared to cobalt catalyst. The Fischer-Tropsch reaction products are commonly divided into separate streams of tailgas, liquid hydrocarbons, and wastewater.
The product from a Fischer-Tropsch reactor typically comprise water vapor, CO
2
, N
2
, unreacted syngas (H
2
and CO), gaseous hydrocarbons (C
1
-C
5
), liquid hydrocarbon (C
5
+) products, and various oxygenates. Generally, most of the water vapor, liquid hydrocarbon products and oxygenates are condensed and separated. This leaves the desired liquid hydrocarbon product and the oxygenate containing wastewater. The liquid hydrocarbon is processed in downstream product upgrading section and waste water is usually sent to a water treatment step.
What remains is the tailgas, which is comprised of water vapor, CO
2
, CH
4
, N
2
, unreacted syngas (H
2
and CO), and vapor hydrocarbon products. The F-T tail gas can be recycled back to the gasification unit or can be recycled to the Fischer-Tropsch reactor inlet or burned as fuel.
Electric power can be generated efficiently in integrated gasification combined cycle (IGCC) systems. For IGCC application, the synthesis gas is fired as fuel to a gas turbine system that drives a generator to produce electric power. Hot turbine exhaust can passed to a heat recovery system to produce high pressure steam which can be expanded through a steam turbine to drive another electric generator to produce additional power. Such IGCC systems generate electricity in an efficient and environmentally sound manner.
The production of chemicals or liquid fuels from a portion of the synthesis gas, such as in a Fischer-Tropsch reactor, in a IGCC system is also well known and has the advantages of common operating facilities and economy of scale in the coproduction of electric power and chemicals. Several references in the background art describe existing technology for combined chemical plant/IGCC power plant operations.
IGCC systems have environmental advantages over traditional power plants that utilize liquid or solid carbonaceous fuels. Oxygen-derived synthesis gas, the gasification reactor product, is an attractive feedstock for the co-production of chemical and/or liquid fuel products and electric power. Integrating IGCC and chemical production plants is desirable, and such IGCC/chemical co-production plants will be installed and operated in coming years because of favorable environmental and economic advantages, and because methods to improve the efficiency and degree of integration of such plants have improved. The invention disclosed in the following specification and defined in the appended claims provides a template for such an IGCC/chemical co-production plant.
SUMMARY OF THE INVENTION
In order to enhance the returns of an IGCC power generation system, it is desirable to make high value by-products in addition to power whenever economically feasible. This invention will make synthetic hydrocarbons in conjunction with power and hydrogen production.
In the instant invention, hydrocarbonaceous fuel, such as coal, oil or gas, is gasified to produce syngas comprising H
2
and CO, scrubbed free of particles, and saturated with water. The syngas can then optionally partially shifted so as to provide the proper H
2
/CO ratio for the downstream hydrocarbon synthesis reactor, such as a Fischer-Tropsch (FT) reactor. The type of catalyst used in the downstream hydrocarb

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