Page 199 - New Trends In Coal Conversion

162 New Trends in Coal Conversion

integration of ITM in Oxy-fuel PCPP has only been studied theoretically. There are
main operation modes for ITM in Oxy-fuel PCPP called 3-end and 4-end, respectively
(see Fig. 6.7). In the 4-end mode, a hot flue gas stream from combustion is recycled
and used as sweep gas on the permeate side. In the 3-end mode, the pressure gradient
across the membrane is generated by a vacuum pump. According to previous studies,
optimal integration is obtained with the 4-end mode and high temperature flue gas
recirculation (Portillo et al., 2013). In this sense, the implementation of ITM with
less energy required the implementation of an high temperature filtration (HTF) system

to protect the membrane, operating in the temperature range of around 850 C(Stadler
et al., 2011).
Another alternative for oxygen production in the Oxy-fuel PCPP is the use of a
chemical looping air separation system (CLAS). This concept is called integrated
chemical looping air separation (ICLAS) (Moghtaderi et al., 2015). In CLAS, the ox-
ygen is separated from the air stream using solid oxygen carriers placed in two
different fluidized beds (oxidation reactor and reduction reactor) at temperatures be-

tween 800 and 900 C (see Fig. 6.8)(Moghtaderi et al., 2015). According to the
ICLAS concept, the oxygen is carried out from the reduction reactor by a fraction
of the hot recycle flue gas stream to the boiler. As in the case of ITM integration,
an HTF system has to be implemented upstream of the reduction reactor. Another

two HTF systems, at temperatures between 800 and 900 C, must be included, one
per reactor, with the aim of recovering most of the oxygen carrier particles and avoid-
ing their emission or feeding to the boiler, respectively.
Oxy-fuel IGCC. Fig. 6.9 shows the scheme of the Oxy-fuel IGCC power plant
concept (Oki et al., 2017). As can be seen in the figure, the hot gas cleanup system
(C/U) is a key technology in this concept. As a major advantage, the syngas is fed
to the gas turbine with higher energy content, increasing the overall energy efficiency
of the plant. The C/U unit consists of a honeycomb desulfuration sorbent operating at

450 C. The implementation of this concept may require two HTF systems (Oki et al.,
2017). One is located upstream of the C/U to increase the availability of the C/U unit
and to avoid obstruction, solid deposition, or abrasion in the sorbent. Another is placed
downstream of the C/U unit to protect the combustion turbine from carryover of sor-
bent particles (Kosstrin, 2017).

6.3 Gas cleaning technologies in IGCC coal gasification

The syngas produced by steam-oxygen coal gasification consists principally of
hydrogen, carbon monoxide, methane, carbon dioxide, and unreacted steam. Nitrogen
will also appear when air is used as the oxygen source. Coal contains a large number of
components that also react or vaporize during gasification so that by-products appear
in the raw gas, often as undesirable contaminants. The volatile matter in coal can
appear in the gas as tar, oil, naphtha, phenols, cresols, and other compounds. Sulfur
is converted mainly to H 2 S, but the gas will also contain COS, CS 2 , mercaptans,
and thiophene. The nitrogen in coal emerges in the gas as NH 3 , HCN, and sulfocyanide