Abstract
Heat exchangers are widely used for heat recovery purposes in many industrial applications such as gasification systems. In a biomass gasification system situated at Melani village in Eastern Cape of South Africa, a significant quantity of heat energy is lost during syngas cooling. Thus, a heat exchanger was constructed and installed in the gasification system for the purpose of heat recovery. Therefore, the aim of this study is to evaluate the performance of the heat exchanger under variable operating conditions for counterflow and parallel flow configurations. The experimental investigation was carried out on a double pipe heat exchanger as the downdraft gasifier system operated on a wood consumption rate of 180 kg/h. The heat exchanger was installed at the exit point of the syngas in the gasifier, and water served as the cooling fluid. Inlet and outlet temperatures of the hot syngas and cooling water (fluids) were measured using thermocouples at variable flow rates. Experimental data were processed using energy equations to determine vital performance parameters (overall heat transfer coefficient, effectiveness, and log mean temperature difference). The findings showed that optimum heat exchanger effectiveness of 0.55 was determined at a mass flow rate of 0.07 kg/s. In addition, counterflow configuration was found to be approximately 14% more effective than the parallel flow configuration. This is attributed to the relative direction of the fluids in the configurations of both flows. The study recommends that double pipe heat exchanger is suitable for recovering heat from the gasification system.
Highlights
Heat recovery is an essential part of any engineering application requiring the efficient transformation of energy from one form to another. is is achieved with the aid of a device called heat exchanger, which is widely used in energy industries, automobile industries, food industries, chemical process industries, and power plants
In the system Johansson biomass gasifier (SJBG), which is the focus of this study, hot syngas when generated from the gasifier will first go through the cyclone for purification purposes. e syngas produced exits the gasifier at a very high temperature because the gasifier is of downdraft type
A tubular heat exchanger of double pipe type was designed, constructed, and integrated into an existing biomass gasification plant for the purpose of recovering heat from the syngas exiting the gasifier at a temperature of approximately 350°C. e custom-built heat exchanger has a water holding capacity of 267 litres. e performance of the heat exchanger was measured during the operation of the gasification plant with a wood supply rate of 180 kg/hr into the gasifier
Summary
Heat recovery is an essential part of any engineering application requiring the efficient transformation of energy from one form to another. is is achieved with the aid of a device called heat exchanger, which is widely used in energy industries, automobile industries, food industries, chemical process industries, and power plants. Heat recovery is an essential part of any engineering application requiring the efficient transformation of energy from one form to another. In energy transformation technologies such as biomass gasification, where heat can be a product or byproduct, heat recovery using heat exchanger is a necessity [1]. Biomass gasification plant generally comprises different systems that make up a unit, namely, feeding system, gasifier/reactor, cleaning systems such as cyclone, and syngas cooling systems such as gas scrubber. Studies on the efficient use of heat exchanger systems for the recovery of waste heat in gasification technology are scarce. In downdraft gasifier very few studies focused on the application of heat exchanger at the cyclone section for heat recovery purposes.
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