Advantages of Gasification
Gasification offers advantages over competing technologies in the processing of a variety of feedstocks into a diverse range of desirable products.
In order to discuss the advantages and disadvantages of any technology, a baseline for comparison must be established. For gasification technology, that baseline is comprised of a range of other technologies that either produce the same products or use the same feedstocks.
The advantages of using feedstocks such as coal or biomass to produce electricity, chemicals, and liquid fuels are well established, revolving around the favorable availability of coal and biomass compared to oil and gas in the United States, and many other countries. Therefore, the commercial technologies with which gasification competes, and to which it should be compared, include coal combustion technologies, direct liquefaction, and biochemical conversion (fermentation) of biomass. The most significant application of gasification technology in the near term is in the production of electricity from coal, so generally the most appropriate comparison for the technology is to other current coal power plant technologies like subcritical and supercritical pulverized coal combustion.
Gasification differs in many areas from these alternatives, and the advantages – and in some cases disadvantages – are discussed in the following sections:
Gasification has inherent advantages over combustion for emissions control. Emission control is simpler in gasification than in combustion because the produced syngas in gasification is at higher temperature and pressure than the exhaust gases produced in combustion. These higher temperatures and pressures allow for easier removal of sulfur and nitrous oxides (SOX, and NOX), and trace contaminants such as mercury, arsenic, selenium, cadmium, etc. Gasification systems can achieve almost an order of magnitude lower criteria emissions levels than typical current U.S. permit levels and +95% mercury removal with minimal cost increase.1 In addition, gasification systems require less water than other technologies.
Carbon Capture Utilization and Storage
Similar to the removal of other contaminants, gasification lends itself to efficient carbon dioxide (CO2) removal because of the high temperature and pressure of the produced syngas. Studies show that in CO2 removal applications, integrated gasification combined cycle (IGCC) plants are more efficient than other commercial technologies. Captured CO2 is prevented from entering the atmosphere through either utilization or storage. The two most common options are carbon dioxide enhanced oil recovery (CO2 EOR), and carbon sequestration. CO2 EOR is a highly practical utilization strategy, in which CO2 is injected underground into mature oilfields to sweep residual oil, where CO2 is stored underground in the process.2 Carbon sequestration involves injecting the CO2 into a deep geologic formation for permanent storage.
Several gasifier designs have been developed to accommodate various grades of coal in addition to wastes and various types of biomass. Gasifiers can also handle pet coke and other refinery products. The potential for using more than one feedstock in a single facility reduces project risk and may extend the project lifespan.
Gasification can be coupled with advanced turbine technology to produce electricity in an IGCC plant. Syngas produced by gasification can also be further processed into liquid fuels (diesel, gasoline, jet fuel, etc.), hydrogen and synthetic natural gas, or a range of fertilizers or other high-value chemicals including anhydrous ammonia, ammonium sulfate, sulfur, phenol, naphtha and CO2 as mentioned above, among many others. Also, slag produced from coal ash can be used in the production of building materials such as cement.
IGCC power plants offer efficiencies similar to or better than other coal power plants. Additionally, in a carbon dioxide capture and sequestration (CCS) scenario, an IGCC power plant is much more efficient than a pulverized coal combustion power plant. This is mainly due to the decreased energy required to remove CO2 from the process streams in gasification as compared with a pulverized coal combustion system.3
Gasification also faces some disadvantages, mostly related to capital costs and availability. Developments in several research areas could improve the long term outlook and potential market share for this technology.