CCGT with coal gasification

In Russia, in 2005, the share of coal in the country's energy balance was about 18 percent (an average of 39% worldwide). According to estimates for 2010-2013, coal reserves at current consumption will last for 100-150 years, while oil and gas only for 30-50 years. Also, the cost of 1 ton of standard fuel ( TUT ) on coal in most cases is the lowest compared to fuel oil and gas. For 2006, the average global efficiency of thermal power plants was 31%. The use of combined-cycle plants with coal gasification will increase the generation efficiency up to two times and reduce pollutant emissions.

Below is a diagram of a power plant using CCGT with coal gasification:

The whole process consists of four separate subprocesses:

  separation of oxygen and nitrogen from air
    gasification of fuel (e.g. coal or biomass) (with air or oxygen at a capacity of over 100 MW)
    synthesis gas purification
    synthesis gas combustion in a gas turbine

The plant uses several types of thermodynamic transformations to produce useful energy. The gas generator is used as a source of synthesis gas (mixture of CO ~ 50%, ~ 25% H2, the rest is СО2, Н2О, СН4). After cleaning, the gas is fed to a gas turbine for combustion. The turbine shaft is connected to an electric generator. Part of the heat of the exhaust gases from the turbine is used to generate steam in the recovery boiler. The steam drives a steam turbine rotating a second electric generator. The IGCC block (see the figure), thus, is similar in structure to the CCGTs that are widespread in the world and natural gas is a reserve fuel for such an installation. The main difference is only in the presence of a system for producing synthetic gas from solid fuel and its integration (due to heat transfer) with a CCGT unit and an air separation unit. It is also possible to use fuel oil, biomass, household waste as fuel. In order to increase the profitability of the synthesis gas process supplied to the turbine, hydrogen and sulfur can be released from it. They can then be used to produce useful products (including fertilizers, ammonia or methanol). Although the removal of hydrogen and sulfur from the synthesis gas stream reduces its calorific value, the profit from the sale of these products compensates for the loss. To protect the environment and to protect the gas turbine from corrosion and erosion from the synthesis gas before burning in the turbine: sulfur dust (in the form of granules, due to the high temperature of the melting process and dust), chlorides, and mercury are removed. Oxygen after separation is used for the gasification process, while nitrogen (not always produced) is mixed with the synthesis gas at the entrance to the combustion chamber. This increases the mass flow rate of the refrigerant through the gas turbine, which raises its output power. In addition, the presence of nitrogen in the flare gas helps to reduce oxide emissions and can reduce the need for water or steam injection. Small amounts of nitrogen can be used to cool the gas turbine. During the separation of oxygen and nitrogen, energy is needed to compress the air - this operation consumes up to 25% of the gross electricity generated by the turbine. The procedure for adding gaseous nitrogen or steam increases the strength achieved in a typical turbine by about 20% compared with the operation of the turbine on natural gas. The synthesis gas, which is a mixture of hydrogen and carbon monoxide, is produced in a sealed reactor in which carbon reacts with steam in the presence of oxygen (pressure 20-50 bar, temperature from 1000 to 1500 K). In addition to the production of synthesis gas in the gas generator, ash and other solid particles are removed. After exiting the gas generator, sulfur compounds, ammonia, heavy metals and even carbon dioxide (the so-called CO2 absorption) are removed from the synthesis gas. As a result, contaminants are removed before combustion in a gas turbine, and not - as in traditional technology - from combustion products. Thanks to the synthesis of high gas pressure before burning, the solution for removing contaminants in IGCC is cheaper and more efficient than used in conventional stations.

The main disadvantage of this technology is its complexity and the high cost of construction. Operation in view of high efficiency and low cost of fuel should be profitable.

As part of the DOE Clean Coal demo project, 3 IGCC coal-fired stations were built in the United States: Wabash River Power Station in West Tere Out, Inidana; Polk Power Station in Tampa, Florida (launched in 1996), and Pinon Pine in Reno, Nevada. Other IGCC coal fired plants are at Alexander (formerly Buggenum) in the Netherlands, Puertollano in Spain and JGC in Japan. The en: Kemper Project in Mississippi is also under construction in the United States.

In Italy, 4 IGCC units were built on the residual oil products: 512 MW at the ISAB refinery in Priolo ( Sicilia ) ^[1] , 575 MW at the Sarroc refinery ( Sardinia ) ^[2] , 280 MW at the refinery Falconara ^[3] and a capacity of 250 MW at the San Nadzaro Refinery ^[4]

• [one]
• Ola Maurstad "An Overview of Coal based Integrated Gasification Combined Cycle (IGCC) Technology"
• Piotr Olszowiec, IGCC: elektrownia na gaz z węgla, Gigawat Energia, 2004 (link not available)
• [2]