Electricity from Pre-Combustion

 Image Courtesy of: Tampa Electric

Gasification technology is the cleanest way to make energy from coal. A typical coal plant emits more sulfur dioxide and nitrogen oxide in a few weeks than a state-of-the-art gasification plant produces in a year.

 

Two principal options are used to make electricity with gasification: 

  • Integrated Gasification Combined Cycle (IGCC)
  • Create Substitute Natural Gas (SNG) from coal or petroleum coke and burn the resulting fuel in a natural gas power plant.                                                                       

                                                                                         

                                                                                                                                          Polk Power Station, Florida. Image Courtesy of Tampa Electric

IGCC

In an IGCC plant, syngas is burned in a turbine to produce electricity.  Excess heat from this process is then captured and used to power a second turbine that makes more electricity. Power plants like this are called “combined cycle” plants. The complete power plant including gasification and combined cycled unit is called an “integrated gasification combined cycle”, or “IGCC”, power plant.

 

Several levels of capture can be used on an IGCC plant. They include:

 

  • 90% Capture -  All carbon in the syngas is converted to CO2 using a shift reaction resulting in nearly all of the CO2 removed. The remaining hydrogen fuel is burned in a special hydrogen turbine to produce electricity. In early 2013, the Texas Clean Energy Project (TCEP) is expected to break ground. The project will capture 90% of its CO2 and produce both electricity and fertilizer.

 

  • 50%-60% Capture - Most, but not all carbon in the syngas is converted to CO2 using a shift reaction. After CO2 removal, the resulting fuel burned in the turbine is a mixture of hydrogen and carbon monoxide. The resulting emissions rival a conventional natural gas fired power plant. This option costs less than the 90% option, and uses industry-standard syngas turbines rather than special ones designed only for hydrogen. In December 2010, Mississippi Power broke ground on Plant Ratcliffe in Kemper County, MS. The 582 MW will capture 65% of its CO2.

 

  • 18%-30% capture- No shift reaction is used to increase the H2 and CO2 content of the syngas. Only the native CO2 in the syngas is removed, with the resulting H2 and CO burned in a turbine. Depending upon the gasification technology and type of coal, the resulting CO2 emissions are reduced by 18% -30% compared to a non-capture IGCC plant. To learn more, please visit Mesaba Energy Project Partial Carbon Dioxide Capture Case (.pdf)>>

 

The amount of  capture levels are a function of the water shift reaction and turbines in the IGCC plant.

 

SNG

Alternatively, syngas produced from coal gasification can be further processed to make substitute natural gas or SNG.  SNG can then be burned in a natural gas combined cycle plant to produce electricity.  These plants often make excess SNG which can then be sold through interstate natural gas pipelines to other gas plants.


Approximately 90% of the carbon dioxide created in the substitute natural gas process can be captured and stored.  This results in a net 50% or more reduction in CO2 emissions compared to the original coal when the substitute natural gas is burned in a conventional natural gas power plant. Read More (.pdf) >>

 

 

Environmental Impacts of Gasification

 Gasification has many environmental benefits:

  • Vastly lower levels of sulfur dioxide, nitrogen oxides, and mercury emissions compared to conventional coal-fired power plants.
  • Carbon dioxide capture technology for syngas has been commercially available for decades.
  • Less solid waste - Solids from gasifiers are half the volume of conventional coal plants. The waste is also vitrified (enclosed in a glass-like substance) and therefore less likely to leach contaminants into the ground.
  • Less water use. IGCC plants use 20% -50% less water than conventional coal plants.