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Alternative Coal Technology


Introduction
General direction of power industry development brings sophisticated and yet costly solutions to answer both fuel saving and environmental concerns. Still, they present an incremental improvement comparable to today’s practice. For instance, traditional sub-critical regenerative steam cycle’s efficiency expected to grow about 2% (absolute) within next 25 years. This increase will be doubled with the introduction of a super-critical regenerative steam cycle. Besides marginal efficiency improvement, suppression of hazardous emissions such as nitrogen oxides (NOx) is achieved using ultra-low NOx combustion technology in combination with catalytic and non-catalytic reduction systems known as SCR or SNCR. This trend of the power plants improvement is likely to dominate the power market for the next 20 years, because it offers lower costs of ownership and maintenance without sacrificing the reliability of plant operation.

The second trend leading to major efficiency increase (about 10% absolute), typically associates with the combined cycles widely advertised by major power industry suppliers (OEM). Implementation of such cycles becomes advantageous for large size units (starting from 400 MWe), where their cost of ownership (in terms of $/kWe installed capacity) is approaching the one for the regenerative steam cycle. Combined cycles offer essential reduction of the major operation expenses, i.e. fuel consumption. Their other benefit is an intrinsic NOx emissions suppression. However, besides rising costs of such plants ownership the reliability of their operation diminishes due to design complexity. The uncertainty of the combined cycles advantages concerns power producers since the cost-effectiveness and reliability of operation prevails in their decision making process. Moreover, this concern grows even higher for the plant owners operating on coal.

In contrast to the above, we offer another, third approach. Its strength is in the minimum cost of retrofit with the simultaneous increase of the efficiency for typical sub-critical regenerative steam cycle that closely matches the one achieved by the best combined cycle. A low risk addition of our equipment realizes an innovative way of energy recuperation within the cycle itself using our patent pending technology. To reach record-breaking NOx reduction we use our patented combustion technology (US patent No 5,501,162).

Coal-Fired Power Plant
Our plant design maintains the general concept of the regenerative steam cycle. Its efficiency increase is achieved by use of an innovative waste heat utilization system for the flue gas and cycle’s regenerative duties improvement. In addition waste heat recovery is also augmented in thermo-chemical processes that allow both non-traditional heat utilization and superior NOx performance. Moreover, waste energy within the cycle is also involved in direct conversion into mechanical and/or electrical energy. As the result, the use of most standard proven equipment is possible. This comprises so-called Electro-Thermo-Chemical system for waste heat utilization.
Combustion system also remains as typical. The advancement is achieved through our ultra-Low NOx burners that typically burners one third of fuel. The rest of the fuel is supplied through specially design fuel injectors. The air required for complete combustion supplied through the multi-stage over-fire air-ports. System allows significant reduction of furnace stoichiometry and effective water walls protection.
As usual, our combustion system design depends on fuel origin and grinding equipment performance. Yet, this dependence is somewhat less than for traditional Low-NOx design. The only requirement for pulverized coal fineness is to have size distribution no less than 75% passing 74 µkm mesh.
For cycles without steam reheat the use of one is necessary in the quantity of about 10% of total steam capacity. For those that have steam reheat an additional installation of 5% of heat transfer surfaces would be required. Proposed plant configuration with installed section of Electro-Thermo recuperation system is shown in Figure 1.


Fugure 1. Installation of the section of TEC unit with combined duties of environmental impact reduction and waste heat recovery


Comparison of the 400 MWe steam cycles using US DOE provisional performance data for the best available technology up to 2025 and the proposed one is summarized in Table 1.
Table 1 Regenerative Cycle Combined Cycle Proposed Cycle
Boiler Type Parameter Sub-Critical Super-Critical Sub-Critical Pressurized Sub-Critical
Capital Cost, $/kW 1,125 1,173 1,385 1,067 1,175
Fuel, $/kW 0.0097 0.0092 0.008 0.0074 0.0075
Heat Rate (MCR), Btu/kW (HHV) 9,077 8,568 7,513 6,870 6,950
Net Power, MWe 397.5 401.8 349.2 398.1 404.5
Efficiency, % 37.6 39.9 45.4 49.7 48.7
Reliability Index (1 to 10)** 8 6 5 4 8
Emissions, Lbs/MMBtu 0.6 0.20* 0.03* 0.03* 0.06

Note: * NOx reduction is achieved using “end-of-pipe” technologies such as SCR or oxygen injection
** Reliability index that introduced here is our own expert opinion and is not a part of DOE analysis

 

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