Korchevoy Yu.P., Maystrenko A.Yu.,Coal Energy Technology Center of National Academy of Sciences of Ukraine and Ministry of Fuel and Energy of Ukraine

The up-to-date state of the Ukrainian power generation industry utilising solid fuel is caused by the following reasons:
- shortage of all types of fuel;
- substantial decrease in the coal quality for the last 25 years to the calorific value of around 16-19 MJ/kg and ash content of up to 33-36 %;
- using of the natural gas or liquid fuel ‘to switch on’ the high ash coal (10-35 % in terms of the overall energy resources consumption);
- significant ‘wear’ of the basic and auxiliary equipment; the most part of them (about 80%) has already spent its service life time;
- ecological problems in areas of a coal mining and electricity production.

This situation is complicated by the fact that, because of the fuel shortage and necessity to regulate a loading of the power systems, steam generators operate at varying power and even shut-downs. Combustion of coals with a high ash content and high sulfur content leads to reductions in the energy unit efficiency with serious impact on the performance and ecology. The solution of these problems can be found by modernizing and reconstructing of the thermal power plants (TPP) using the novel high effective coal technologies to ensure:
- essential improvements in the engineering and economic performances compared to pulverized coal-firing boilers;
- possibility to utilize a raw coal with different metamorphism degree and ash content of up to 50%;
- elimination of natural gas and liquid fuel from a fuel processing;
- significant reductions in emissions and discharging of harmful products into the environment;
- possibility to operate in flexible loading regime providing the higher ecological and economic performance;
- complete utilization of wastes.
The following coal technologies meet these primary requirements [1-3]:
- circulating fluidized bed (CFB) combustion technology;
- pressurized fluidized bed (PFB) combustion technology and pressurized circulating fluidized bed (PCFB) combustion technology for combined cycle plants (CCP) using solid fuels;
- gasifications in PFB and PCFB for CCP using solid fuels.

The CFB coal combustion technology has already passed through the basic testing stage and has been widely used in TPP and some utility units throughout the world. As to the Ukraine is concerned, the adaptation of this technology to the domestic coal should be made before practical applications take place.

Broad investigations have been established in the Coal Energy Technology Center of the National Academy of Sciences of Ukraine and Ministry of Fuel and Energy of Ukraine using both laboratory scale prototypes and pilot units with the range of heat power from 0.05 MW to 1.2 MW [1, 2]. These studies have been resulted in specification of optimal technological parameters of CFB combustion (temperature of boiler elements, particle size, primary/secondary air ratio, calcium/sulfur ratio in initial fuel) of high ash anthracite schlamm, Donetsk lean coal, gaseous coal, long-flame coal, Lviv-Volyn gaseous coal and Alexandria brown coal in circulating fluidized bed. This database provides the maximum rate of a coal conversion with minimized sulfur and nitrogen oxides emissions. The results obtained have been used in development of advanced designs of CFB boiler units with output of up to 160-670 tons per hour including boiler units with output of steam production of 670 t/h (Starobeshivska TPP), 260 t/h (Myronivska TPP), and 250 t/h (Nesvetay ТPP).

The coal combustion and gasification technologies in PFB and PCFB for CCP that use solid fuel have the efficiency that is by 4% - 8% higher than that of the CFB energy units; in addition, the former technologies bring less ecological impact and require less specific quantity of metal per unit . These novel technologies are at the stage of pilot-scale testing and demonstrating in different countries including the Ukraine.
The specific features of the technologies developed at CETC are two-stage process (pyrolysis-gasification, pyrolysis-combustion) with thermocontact pyrolysis of raw coal in lowered bed and combustion or gasification of the coke-ash residue in a PCFB[] In number of cases, a fine-fraction of a solid fuel comes in return pass while a large fraction is fed into pyrolyser or at the top of the PCFB furnace. These technologies have been tested in laboratory conditions under the pressure of up to 2.5 МPа and in pilot facilities running under atmospheric pressure conditions. Finally, the technologies will be used in the demonstration facility CFB-1.0 with a heat capacity of about 10 МW under pressure of 0.8-2.5 МPа which is constructed at CETC.

The thermal processing of coals under pressurized conditions have demonstrated that pyrolysis-gasification and pyrolysis-combustion technologies in PCFB are very effective for Donetsk gaseous, long flame and brown coals. As to anthracites and lean coals is concerned, the PCFB combustion with separation of fine and large size fractions of coal is more preferable. As soon as the PCFB technology will be comprehensively tested at the CFB-1.0 demonstration facility, it is planned to build the 100 МW PCFB demonstration unit with in-cycle combustion of high-ash coal. Its commissioning is expected in 2010-2015 years.