PROBLEMS OF GAS EXHAUST DUCTS OPERATIONAL RELIABILITY OF MUNICIPAL SOLID WASTE INCINERATION PLANTS AND WAYS TO SOLVE THEM

Abstract

The work is devoted to research on creating conditions for the safe operation of gas exhaust ducts of solid waste incineration plants. The operation of these ducts is characterized by difficult conditions that lead to their corrosion destruction, especially the last section of the duct - the chimney. The development of measures for the chimneys corrosion protection in the case of using deep flue gas heat recovery systems requires special attention due to the likely high humidity and high chemical aggressiveness of these gases. The purpose of the study is to analyze the indicators of thermal and humidity state in the chimney mouth of a waste incinerator plant with a water-heating boiler in its different operation modes under the conditions of using the technology of deep cooling of exhaust gases and thermal methods of preventing condensation in gas exhaust ducts. The main objectives of the study were to perform thermal calculations of the boiler with the proposed heat recovery system and to establish patterns of change in the main thermal and humidity indicators at the mouth of the reinforced concrete chimney under different boiler operating conditions. Known thermal calculation methods of heat and power plants installations and the results of our own research on heat exchange during deep cooling of exhaust gases were used. The results on the effectiveness of using the methods of heat and humidity treatment of flue gases after heat recovery to prevent condensation in the reinforced concrete chimney of the considered boiler are presented. Three thermal methods were investigated: bypassing a part of the boiler exhaust gases past the heat recovery system, drying the cooled gases in a gas-heater, and mixing a part of the air heated in the system with these gases. The regularities of changes in thermal and humidity indicators in the chimney mouth are established and the limits of effective application of each method under different conditions are determined. It is shown that the bypassing method is not effective for preventing condensation under all the conditions considered; the drying method gives positive results for preventing condensation in the chimney mouth at high boiler loads corresponding to low ambient temperatures (t_amb < -5°С), high gas temperatures at the boiler outlet (t^g_inp > 200°С) and at the levels of heating of cooled gases in the gas-heater Δt, which mostly exceed 30°С; the air method at the share of σ (up to 30 %) of the mixed air ensures the prevention of condensation in the chimney mouth in boiler operating conditions close to the nominal. It is also shown that the heat consumption for the implementation of the air method is the lowest compared to the other two methods.