Studying the Effect the Yield of Sulfur Dioxide and Chlorine-Containing Components on the Toxicity of Combustion Products from a Gas-and-Oil-Fired Boiler Operating on Off-Design Fuel

Abstract

In the fuel oil production technology, the lower fractions from the petroleum refining process form cracking residues. Under certain conditions, cracked fuel oil suitable for use in steam power-generating boilers at thermal power plants can be obtained by mixing cracking residues and high-quality furnace fuel in appropriate proportions. In such circumstances сracked fuel oil is characterized as a backup fuel, the fraction of which in a power plant’s total fuel balance is determined by full-scale experiments individually for each boiler unit to ensure the permissible environmental indicators of the power unit operation. The paper presents the results from a study aimed at determining possible use of low-sulfur cracked fuel oil with a content of chloride salts no less than 4.886 mg/kg as the primary fuel for a BKZ-420-140 GM gas-and-oil-fired boiler. The possibilities of improving the environmental performance of boilers burning cracked fuel oil are evaluated. The contents of hydrogen chloride and sulfur dioxide in the boiler flue gases are determined depending on the excess air coefficient variation range at the combustion chamber outlet. The maximum ground-level concentrations of sulfur dioxide and hydrogen chloride in the cracked fuel oil combustion products in different boiler operation modes are calculated. The annual quantities of chloride components emitted into the environment are determined. The mechanisms through which the amounts of hydrogen chloride and sulfur dioxide emitted into the environment can be kept within the permissible limits during boiler operation at full load are analyzed. It is pointed out that decreasing the content of free chlorine in the flue gases from boilers burning cracked fuel oil is a measure that helps to reduce significantly the possibility of generating carcinogenic polychlorinated dibenzo-n-dioxins and dibenzofurans, one of which has been adopted by the United Nations as the international toxic equivalent. The introduction of environment protection technologies at existing power plants involves high financial costs and long payback periods due to rather low charge rates for emissions of toxic compounds into the atmosphere. The amendments made to the Federal law “About Environmental Protection” and certain legislative acts of the Russian Federation stipulate, from the beginning of 2015, the development of handbooks on the best available technologies for the national economy sectors, the use of which at existing and newly built thermal power plants will contribute to making the operation of power units safer for the environment. As a separate measure, the possibility of exempting power-generating enterprises actively implementing environmental protection measures from environmental charges is considered.