Study of Pressure drop in Heat Exchangers

Abstract

Heat exchangers are frequently used in industry especially in steam and gas turbines power plants, as air pre-heaters or economizers and the like. These are mainly used to recover part of the thermal energy in exhaust and flue gases. The measure of performance of these equipments is usually given as a heat ratio which is a measure of the heat recovered from the exhaust. Heat exchangers suffer from pressure losses due to the resistance to fluid flow through the passages on both sides of the exchanger. The pressure drop means in most cases, a loss in the useful work output. In this research the investigation concentrates on the thermal ratio and the pressure drop in heat exchangers applied in existing power stations. Three of the largest power stations in Sudan are examined: namely: i.Khartoum Refinery Company ( at Elgili). ii.Khartoum North Thermal Power Station. iii.Kenana Sugar Factory. Temperatures and pressures were measured and calculations were carried out and the results were presented, and discussed. Kern methods for calculating the pressure drop were examined using data obtained from unit (2) phase (I) in Khartoum North thermal power station. The results obtained revealed that: a)The thermal ratio of heat exchangers, in addition to their dependence on the thermal properties of the material from which they are made, was affected by the method of design and the inlet conditions. The results of the tests showed that for the shell and tube type of heat exchanger used in Kenana Sugar Factory, the thermal ratio was 0.52 while it was about 0.777 for the rotary heat exchanger used in Khartoum North thermal power station, phase (II) unit (4). b)The least pressure drop amounting to about (190 pa) i.e. about 1.6% of the inlet pressure, when using bar heaters as in Khartoum Refinery Company, and the highest pressure drop was (1830 pa) i.e. about 7.7% of the inlet pressure drop, when using Rotary heat exchangers, as in phase (II) unit (4) of Khartoum North thermal power station.