Hardware and Software of Automatic Control System of Fuel Combustion Process in Low and Medium Power Boilers. Part 1. Method and Hardware

Abstract

In Ukraine today there are more than 6000 boiler plants with a heating capacity of up to 1 Gcal/h with an efficiency of about 70 %, requiring replacement or modernization, 40 % of boilers are operated with an efficiency of less than 82 %, about 11000 boilers with a capacity of 100 kW to 1 MW have been in operation for over 20 years. Although the part of these boilers in the municipal heat power system of Ukraine does not exceed 14 %, the projected savings in natural fuel in these boilers is more than 130 million cubic meters per year. Thus, increasing the efficiency of the fuel combustion process in small and medium power boilers is an urgent task at the present time.
 The article presents the results of creating a method and hardware that implements it, to increase the speed and reliability of monitoring the process of fuel combustion in boiler units based on measuring the concentration of residual oxygen in exhaust gases. The developed method is implemented by stepwise correction of the ratio of the air-fuel mixture entering to the furnace of the boiler for combustion, according to feedback signals from a broadband oxygen sensor manufactured by Bosch, located in the outgoing channel.
 The air-fuel ratio control with automatic adjustment of the blower fan speed depending on the amount of fossil fuel supplied for combustion ensures low-toxic combustion of fuel with low emissions of nitrogen oxides and carbon monoxide, and high efficiency. Additional use of a variable frequency drive in the combustion control system allows to reduce energy consumption by 30-40 %, eliminate starting currents and motor overloads, reduce mechanical wear of equipment, increase the service life of contact switching equipment. In general, the developed fuel combustion control system allows to optimize the fuel combustion mode, taking into account the actual conditions, operating modes of the boiler unit and fuel characteristics; to reduce specific fuel consumption by at least 10%; to reduce the level of emissions of nitrogen oxides up to 40 % and carbon monoxide up to 50 %; to increase the efficiency by at least 5 %; qualitatively to simplify the work of the boiler maintenance personnel.