Advantages of Gasification
This page introduces the main environmental benefits of gasification compared to competing technologies. Gasification systems offer advantages over competing technologies in the processing of multiple feedstocks into a variety of desirable products in three main environmental areas: criteria emissions reduction, the potential for carbon dioxide emissions reduction and water use reduction.
Criteria Emissions Control
Gasification has inherent advantages over combustion, due to the ability of the technology to achieve extremely low emissions of sulfur and nitrogen oxides (SOX and NOX) in addition to low levels of particulate matter and other contaminants such as heavy metals. The higher temperature and pressure process streams involved in gasification also allow for easier removal of CO2 for geological storage or for sale as a byproduct.
In combustion, air and fuel are mixed, combusted and then exhausted at near atmospheric pressure. In gasification, on the other hand, oxygen is normally supplied to the gasifiers and just enough fuel is combusted to provide the heat to gasify the rest. Since air contains a large amount of nitrogen along with trace amounts of other gases, which are not necessary in the combustion reaction, combustion gases are much less dense than synthesis gas (syngas) produced from the same fuel. Pollutants in the combustion exhaust are at much lower concentrations than that in syngas, making their removal more difficult and expensive.
CO2 Emissions Reduction
Gasification technology enables relatively efficient capture and storage options for CO2 in power, chemical, and liquid fuel production compared to conventional technologies, making it a potential means of reducing the carbon footprint of these industries in the future. The gasification process allows for high pressure, low volume removal of the CO2 from the syngas prior to use in gas turbines for power, or conversion into other end products.
Gasification also offers some water-saving advantages over other technologies for producing electricity from coal. Regions with limited water resources, typical of many parts of the western United States, could conserve resources by meeting increasing electricity demand with integrated gasification combined cycle (IGCC) generation. Many of these areas have good coal resources and a need for new generating capacity.
In an IGCC setting, water consumption is dramatically reduced compared with pulverized coal (PC) plants due to the reduced reliance on steam on a consistent electrical output basis. Since the syngas produced by the gasification process is combusted in a gas turbine, steam is not used as the primary means of transferring the energy from the coal to rotational energy. Steam is only used to recover the heat from the gas turbine exhaust in a Heat Recovery Steam Generator (HRSG). This reduces the steam system size required for an IGCC plant significantly, compared to a PC plant of similar electrical output. There are some additional processes in an IGCC plant which require water, that are not necessary in a PC plant. However, these processes typically consume less water than the amount saved in the generation of steam for power production, giving IGCC an advantage in water use, which is increasingly important factor in the selection of a power generating technology.