Agriculture Reference
In-Depth Information
H 2 O + CO CO 2 + H 2
(8)
The table shows that the emissions of NO x remained unchanged after the introduction of
raffinate. This may be explained on the basis that both the coal (1.62%) and raffinate (1.6%)
contain almost the same nitrogen content on as received basis.However, emissions of SO 2
decreased after raffinate introduction which again explains the possibility of formation of
H 2 SO 4 by the reaction of SO 2 with water present in raffinate.
5.2. Co-Firing of Raffinate with Natural Gas
During previous test of co-combustion of coal with raffinate, agglomeration occurred
very quickly possibly due to difficulty in properly controlling the bed temperature. So, it was
decided to conduct controlled bed temperature test with raffinate and natural gas instead of
coal as bed temperature can be better controlled with gas firing than coal firing. Also as the
gas burner fires into the combustion chamber (acting as plenum chamber) to the fluidized
bed, flue gas coming from the distributor is at a higher temperature as compared to air and
thus will have a higher volumetric flow. This might exert a higher force that will break up the
loose agglomerates and therefore agglomeration temperature might be higher than that
achieved with raffinate and coal co-firing.
After getting stable bed temperature with natural gas (firing rate at 32kW) raffinate was
introduced into the bed at a flow rate of 2.29 l/h (3 kg/h). Experimental conditions before the
raffinate introduction were noted to be BT = 800 °C and BP = 261 mmWg.
After around 10 minutes, raffinate feed was stopped due to low bed pressure. Total
amount of raffinate fed into the bed during this period was 0.38 litres (0.5 kg) which
translates into around 6.2% raffinate in the sand. The burner was kept running so that gas
coming from the combustion chamber was still at high temperature. It was observed that BT
went up slowly and BP went down to 100 mmWg. The bed and freeboard temperature and
bed pressure variations during the experiment as a function of time are plotted in Figure 12.
Three major differences were noted between coal-raffinate co-firing and gas-raffinate co-
firing.
1.
With gas-raffinate bed slumped within ten minutes and with lesser amount of
raffinate going into the bed as compared to coal-raffinate.
2.
Bed temperature went up instead of going down as in the case of previous
experiment with coal and raffinate
3.
Freeboard temperature was lower than the bed temperature as opposed to coal-
raffinate tests.
After 6.8 minutes of the raffinate stoppage, burner was stopped but fan was kept running.
BP started going up and restored to its original value. Thus it can be concluded that
agglomerates formed at higher temperature broke down to individual particles when BT
dropped. With natural gas-raffinate co-firing bed slumped quickly, in lesser time and with
lesser amount of raffinate feeding into the bed as compared to coal-raffinate co-firing. This is
possibly due the fact that coal mineral matter, due to the presence of calcium, helps
preventing the agglomeration and increases operational time.
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