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Demonstration and Deployment development of CCT and CCS Project:
 

EUROPEAN UNION

 
 
 

Under the EU TREC-STEP BHEL CCT CCS project two important demonstration projects have been implemented by the project partner Bharat Heavy Electricals Limited BHEL, Trichy.

Bio-mass Co-firing Demonstration:
Biomass Co-firing is the process of replacing part of the coal supplied to a power station or boiler with ‘carbon neutral’, renewable biomass. Biomass is considered ‘carbon-neutral’ because it returns the CO2 that was absorbed from the atmosphere as the plants grew. Since biomass can replace between 20 percent and 50 percent of coal, this technology has an enormous potential for reducing CO2 emissions. However, there are a number of significant challenges which prevent the more widespread use of biomass. Compared to coal, biomass is less dense and its use requires the plant’s fuel feed systems to be able to handle much larger volumes of fuel. There are also milling issues which can affect flowability of the mixture. Moreover, there is the issue of feedstock availability.

In order to execute the project, BHEL designed and made modifications and additions to the existing facility at the Coal Research Centre’s Solid Fuel Burning Test Facility. A biomass silo was designed, fabricated and erected. A variable drive biomass screw feeder was procured and fitted on to the system. A ball mill was installed and trials carried out with rice husk and Julie flora cut waste. The programme also experimented with co-milling of different biomass products along with coal in order to ascertain what the best system for creating the right mix that would ensure that the system was giving the desired results.

The trials have been successful. The critical hurdle of co-milling wood pellets with coal has been overcome and the co-fired flame temperature (with 10-20 percent wood pellets) is close to that of pure coal firing. Fouling and slagging characteristics have been favourable and the deposits can be cleaned easily. BHEL is now exploring taking these trials to the next level.
 

Bio-mass Co-firing Demonstration:
Air has a high (78 percent) content of nitrogen. During combustion with air, most of the nitrogen passes through the process unchanged, with only a small fraction being converted into oxides to form NOx gases. A typical power plant exhaust gases contain about 75 percent nitrogen, which must be removed to create a CO2 stream for storage. This separation is energy-intensive and expensive. Oxyfuel combustion significantly changes how the combustion is conducted. It uses oxygen instead of air, thus eliminating nitrogen from the oxidant gas stream and producing a CO2 enriched flue gas. This flue gas is ready for storage after the water has been condensed and other impurities have been separated out.

Oxyfuel technology has been developing steadily since the late 1990s. Pilot-scale oxyfuel demonstrations have so far confirmed that plant operations can be effectively switched from air-firing to oxyfuel firing and a highly enriched CO2 flue gas produced for transportation and storage. Moreover, the process results in a significant reduction in NOx emissions. Another significant advantage of Oxyfuel combustion is that it offers possibilities of retrofitting the existing fleet of modern pulverised coal-fired power plants for CO2 reduction. Oxy fuel combustion technology demonstration has been implemented at BHEL Coal Research test facility.

The Oxy-fuel tests have been carried out at the Coal Research Centre’s Solid Fuel Burning Test Facility. BHEL Coal Research team has designed a special burner for oxy-fuel combustion. In addition, a cyclone assembly has been fitted to remove ash particles from the exhaust flue gas. A heat exchanger was added to cool the flue gas and an induced draft fan installed to pump flue gas into the burner along with oxygen. The project has had to mount a probe system in order to measure the heat flux so that it could be compared with the one for conventional firing. An oxygen transportation line has been integrated as has been a cooling water line for supplying water to the heat exchanger and heat flux sensor. Dampers and orifice plates were fabricated and installed in order to control and monitor the exhaust flue gas. Extensive tests using this trial apparatus have been carried and once again, the results have been encouraging. Successful recirculation of the flue gas from the chimney has been achieved as has been the transition from air-coal combustion to oxy-coal combustion. NOx and SO2 emission levels have been quantified for the purpose of comparisons and the optimum flue gas circulation for a favourable flame temperature determined.