John, Randy C. (Shell Development Co.) | Jordan, Kenneth G. (Shell Offshore Inc) | Kapusta, Sergio D. (Overseas Planning) | Young, A.L. (Humberside Solutions Ltd.) | Thompson, W.T. (Royal Military College)
Siegmund, Gerit (BEB Erdgas und Erdoel GmbH) | Bruckhoff, Wolfgang (BEB Erdgas und Erdoel GmbH;) | Schmitt, Guenter A. (Iserlohn University of Applied Science) | Pankoke, Udo (Iserlohn University of Applied Science) | Sadlowski, Bernd (Iserlohn University of Applied Science)
coal gasification, reducing atmosphere, hydrolysis, chlorination, sulphidation, corrosion, silicon carbide, filters, strength.
The fuel gas derived from coal gasification contains gaseous species such as CO/CO2, Hz/H20 and CH4, as well as gaseous compounds of sulphur, nitrogen and chlorine and entrained solids of char and ash. On exiting the gasifier vessel temperatures can be between 673K and 1273K with a ~02 as low as 10-2satm. and pS2 as high as lo-7atm. making the environment extremely reducing and sulphidising. In this area, high temperature particle control filters are required to meet environmental and turbine equipment requirements. The aim of this research was to evaluate the effect of a simulated gasification atmosphere on the mechanical properties of a clay-bonded Sic by considering the thermodynamic stability of the possible gas and solid chemical reactions. Temperatures between 873K and 1273K were employed for up to 200 hours with 3- point bend tests used to measure changes in strength. Three atmospheres (A, B and C) were employed to investigate the effects of sulphur, water vapour and chlorine respectively. Analytical techniques (e.g. SEM, XRD and EDX) coupled with complex thermodynamic calculations allowed the investigation of the corrosion mechanisms for these materials under simulated gasification conditions. It was found that a severe strength degradation of the filter material occurred due to volatilization of clay-binder constituents and this volatilization was accelerated by the addition of water vapour. Micro-crack formation due to stresses induced by devitrification and cooling also severely reduced the room temperature fracture strength.
Pressurized fluidized bed combustors (PFBC) are being modified throughout the world to produce a combined cycle of both steam and gas turbines. These systems combine the gasification of coal to produce carbon monoxide and hydrogen, together with combustion of the residual char; the gas being used to drive a gas turbine and the char burned to raise the high-temperature steam required to drive a steam turbine.
On exiting the gasifier, the environment is extremely reducing and sulphidiizing due to the low levels of oxygen and high levels of sulphur (~02 = 8.10.ZSatm, pS2 = lo-Ii atm [873 K])l and high levels of CO, CO2, H2 and sulphur-containing gases. A projected gasifier gas composition at 850 K and 19 bar, prior to gas treatment, is shown in Figure 1 l. The composition of a particular gasification atmosphere will depend on a number of factors including reaction conditions, type of coal feed stock, coal pretreatment, heat supply, reactor configuration and gas purification.
The hot, pressurized gases from the gasifier can reach temperatures of approximately 1273 K and carry heavy loads of dust composed mainly of coal ash. Unremoved, this dust would be very damaging to a gas turbine, causing blade erosion and fouling. Pre-cleaning cyclone systems remove 90-95% of the dusts, reducing the content to the order of 10,000 ppm (wt.). The expansion gas must be essentially dust-free (<5ppm (wt.)) and not contain particulates of >2um diameter. Thus, ceramic filters are used to reduce the dust concentrations to a level adequate for an economic gas turbine life.