The purpose of modernizing the Pp-1050-25-545 KGZh (P-50R) boiler is to reduce the emissions of nitrogen oxides (NO x ) to levels consistent with modern requirements. The following engineering steps were taken, with liquid slag removal from the boiler, to attain NO x levels of 700 -750 mg/m 3 for operation with coal and 125 mg/m 3 for operation with natural gas:-three-stage combustion with natural gas as the reducing fuel (~15% thermal) burning in the recirculating gases; and, -use of low-emission coal-dust burners with dust feed at high concentrations, overflow burners, and tertiary draft nozzles to lower the amount of excess air in the active combustion zone.The NO x level was further reduced to 570 g/m 3 (just for operation with coal) by using a selective noncatalytic nitrogen oxide reduction system with injection of ammonia (NH 3 ) vapor into the boiler in a zone with temperatures of 950°C.Between 1963 and 1967 the Podol'sk Machine Factory manufactured seven P-50 boilers. Three of these were included in the double-units of the 300 MW Kashira GRÉS (Kashira State Regional Electric Power Plant). The last P-50 boiler at the Kashira plant was brought into operation in 1968.In 1995 an order was placed by the Kashira GRÉS at the Podol'sk Machine Factory to develop a project for reconstructing the boilers, aimed at increasing their steam production from 950 to 1050 tons/h in order to maintain a unit power of 330 MW. The letter "R" was added to designate the new, reconstructed Pp-1050-25-545 KGZh boiler (i.e., P-50R).This project involved a change in the design of the baffle heating surfaces: horizontal baffles were replaced by suspended vertical ones; furnace baffles (side walls) were installed in the combustion chamber, mounted in the upper part of the front wall; the surface area of the economizer was increased; the bypass pipes were modified and a hot box was set up; and, the ceiling suspension system was modified. The reconstruction project for the boiler installation also took into consideration the possibility of startup and shutdown of the boiler at variable pressure and included improvements in the startup unit. To do this, a number of changes in the boiler design were made on the recommendation of VTI:-a flush separator unit, consisting specifically of flush separators and a prefabricated vertical collector, was specified; -special dividers, or "distributors," were used for separating the flows of steam-water mixture from a given boiler. In order to introduce these dividers, changes were made in the framework piping for the wall baffles in the lower and middle radiative sections (LRS and MRS) of the burner.The new P-50R boiler was manufactured at and delivered to the Kashira GRÉS, but not set up because of a lack of funds. After 12 years a decision was made to install it.In order to evaluate the state of the equipment, the metal in the structural components was analyzed; this showed that the bulk of the heating surfaces had been subjected to considerable corrosion. It was necessary to replace entirely the
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