DESIGN AND IMPLEMENTATION OF AN AUTOMATIC CONTROL SYSTEM TO AVOID FOULING IN PIPES WITH BLOW DOWN HEAT RECOVERY IN STEAM BOILERS

Abstract

Abstract The aim of the present work is to solve the problem of fouling in boiler pipes and improve energy efficiency of steam boilers in the south refineries company, Al-Basrah province, Iraq. An automatic control system with a novel electronic circuit has been proposed to achieve this aim. This system consists of an on-line conductivity sensor and a conductivity monitor connected to an additional resistance to measure the concentrations of dissolved solids in boiler water. A square wave feedback has been employed to determine the levels of solid concentrations and controls the surface blow down process through electronic circuit. This circuit consists of a D.C power supply, an amplifier, a rectifier, comparators and a driver sub-circuits for solenoid valve. The driver sub-circuit consists of two transistors and three relays. The solenoid valve is used with throttle valve to control the flow rate of boiler blow down water. Two flow meters are used to measure blow down and feed water flow rates. The design and implementation of a heat recovery unit is also included. It consists of a heat exchanger (shell and coiled tube) type used to recover heat energy from blow down water. To measure the inlet and outlet temperatures of feed water and blow down water, four (k-type) thermocouples were used. A pump was used to pump feed water from the storage tank in to the boiler. To automatically control water level inside the boiler two electrodes (water level sensor) were used integrated with the float less level switch circuit. The experimental results proved the effectiveness of the innovative control system in improving boiler efficiency and in fouling control through enhancing the blow down process and reducing indirect losses. The blow down quantity reduced from 2244.897 kg/h to 1111.111 kg/h. Which provided 27210.864 kg/day of blow down water. Hence, saved 158450201.2 ID/year or 83.16% of the energy lost with blow-down water can be recovered using heat-recovery unit with an energy saving of 103411.8 MJ/day. Which will save a mass of fuel equals to 482.46 ton/year. The automatic control system proved to be a good solution for saving energy and reducing harmful emissions to the environment and it contributes to the maintenance of sewage pipes from damage caused by the heat of discharged water.