Low-temperature Heat Recovery System Research Articles

Enhanced heat transfer in a phase change energy storage with helical tubes

Solar collectors integrated with phase change materials (PCM) store heat energy for later use. However, the settling of PCM prolongs the melting duration in a vertical cylindrical container. Hence, selective methods are required to alleviate such solid PCM settling issues. A helical heat transfer tube (HTT) can improve melting by increasing the contact surface. The present research studies the charging and discharging of PCM using three helical coil HTT configurations: fully expanded, semi-compressed, and fully compressed. The fluid flow rate and inlet temperatures are 20 LPH and 80 °C, respectively. The simulation involves two-dimensional numerical modeling using Ansys Fluent software and the finite volume method with the enthalpy-porosity technique. The fully compressed HTT melt settled PCM inside the vertical cylindrical container faster. The experimental results show that using a fully compressed HTT reduced the melting time by 50 % compared with a fully expanded HTT of 160 min due to the effective melting of settled PCM. Its peak heat stored, energy efficiency, Nusselt, Stefan, and Rayleigh numbers are 356 kJ, 34.8 %, 75.34, 0.47, 2.8036 × 107, respectively. The compressed HTT is a practical design suggested for solar collectors and low-temperature heat recovery systems, which demand a fast heat storage rate.

Optimisation of simple and regenerative organic Rankine cycles using jacket water of an internal combustion engine fuelled with biogas produced from agricultural waste

Internal combustion engines have a very important place in biogas production facilities to convert biogas energy to electricity. Unfortunately, although intense studies on improving internal combustion engine efficiencies by operational optimisation methods, serious progress is not achieved yet. However, there are many ways to improve the performance of these engines apart from structural optimisation methods. One of the most important ways is to utilize by integrating jacket water used to cool the biogas fuelled internal combustion engines into the new generation low-temperature heat recovery systems like organic Rankine cycles. In the present study, simple and regenerative organic Rankine cycles were optimised to improve the overall performance of an biogas fuelled internal combustion engine by using the jacket water which is released into the atmosphere after cooling the engine. Also, the energy, exergy and environmental aspect of these systems are evaluated. Finally, exergoeconomic analysis for both systems are conducted, and then payback periods of both systems are determined. As a result of the study, the maximum net power, thermal and exergy efficiencies of the simple organic Rankine cycle was calculated as 42.14 kW, 11.47 % and 63.27 % respectively, while the maximum net power, thermal and exergy efficiencies of the regenerative organic Rankine cycle are found as 45.3 kW, 12.34 % and 68.02 %. In addition, it is observed that the maximum power production obtained from the regenerative organic Rankine cycle corresponded to nearly 630 kg CO2/h emission reduction. The best payback period value is also calculated as 7.37 years in the simple organic Rankine cycle.

Low Temperature Energy Recovery Designs

This article discusses low temperature energy recovery systems that are being installed on three Federal buildings in the Washington, DC, area. The three projects discussed use simple systems that deliver low cost heat to buildings in innovative ways. Each uses a source of low temperature heating available from within the building to reduce fossil fuel use. One system recovers heat from the ventilation return air to heat water for the hydronic reheat loop serving variable air volume boxes in the building. The second system recovers heat from an attic space below a plywood roof deck covered with asphalt shingles to heat a domestic hot water loop for a barracks. The third system recovers heat from the solar re-roofing of a building to supply heated air for swimming pool heating and for a heating, ventilating, and air conditioning system. The purpose of this article is to demonstrate the versatility of these low temperature heat recovery systems.

Experimental investigation on heat recovery from condensation of thermal power plant exhaust steam by a CO2vapor compression cycle

SUMMARY In this paper, a method that utilizes CO2 vapor compression thermodynamic cycle to recover low-temperature heat from exhausted water steam of fossil fuel thermal power plants is reported. Experimental investigation was carried out to study the characteristics of low-temperature heat recovery by liquid CO2 evaporation process from vacuum exhausted steam condensation occurring at the turbine exit. Furthermore, measured heat recovery performances over one whole year are presented and discussed. Experimental results show that the present heat recovery process by CO2 vapor compression cycle is able to operate stably. The yearly averaged water temperature at the CO2 condenser outlet was measured at 87.5 °C with a COP value above 5.0. This high energy efficiency ratio is found to be mainly due to two factors: the transcritical CO2 vapor compression and steam condensation phase change occurring on the CO2 evaporator. The findings from this paper provide helpful guidelines for low-temperature heat recovery system design and improving fossil fuel utilization efficiency. Copyright © 2013 John Wiley & Sons, Ltd.

Solar energy powered Rankine cycle using supercritical CO 2

A solar energy powered Rankine cycle using supercritical CO 2 for combined production of electricity and thermal energy is proposed. The proposed system consists of evacuated solar collectors, power generating turbine, high-temperature heat recovery system, low-temperature heat recovery system, and feed pump. The system utilizes evacuated solar collectors to convert CO 2 into high-temperature supercritical state, used to drive a turbine and thereby produce mechanical energy and hence electricity. The system also recovers heat (high-temperature heat and low-temperature heat), which could be used for refrigeration, air conditioning, hot water supply, etc. in domestic or commercial buildings. An experimental prototype has been designed and constructed. The prototype system has been tested under typical summer conditions in Kyoto, Japan; It was found that CO 2 is efficiently converted into high-temperature supercritical state, of while electricity and hot water can be generated. The experimental results show that the solar energy powered Rankine cycle using CO 2 works stably in a trans-critical region. The estimated power generation efficiency is 0.25 and heat recovery efficiency is 0.65. This study shows the potential of the application of the solar-powered Rankine cycle using supercritical CO 2.

96/06316 Advanced burner design for pulverized coal combustion in utility boilers

As part of the Combustion 2000 Program of the US Department of Energy, advanced low-emission boiler systems are being developed for future coal-fired power plants. These plants will be extremely clean, highly efficient and economic, by employing emerging and state-of-the-art technologies. The emissions of SOx, NOx and particulates from the plants will be much lower than the current new source performance standards (NSPS), and the net plant efficiency of generating electricity will be higher than that of today's pulverized-coal-fired utility plants. The high plant efficiency results in low fuel use and reduced emission of gases (CO2) associated with global warming. At present, engineering development of advanced systems is being conducted by three industry teams. The development work includes new emission control technologies, state-of-the-art boiler designs and low-temperature heat recovery systems for improved plant efficiencies, systems for improved ash disposability and reduced waste generation, and optimum system integration and plant controls. The technologies considered by these teams for low-emission boiler systems are discussed.

Advanced coal-fired low-emission boiler systems

As part of the Combustion 2000 Program of the US Department of Energy, advanced low-emission boiler systems are being developed for future coal-fired power plants. These plants will be extremely clean, highly efficient and economic, by employing emerging and state-of-the-art technologies. The emissions of SO x , NO x and particulates from the plants will be much lower than the current new source performance standards (NSPS), and the net plant efficiency of generating electricity will be higher than that of today's pulverized-coal-fired utility plants. The high plant efficiency results in low fuel use and reduced emission of gases (CO 2) associated with global warming. At present, engineering development of advanced systems is being conducted by three industry teams. The development work includes new emission control technologies, state-of-the-art boiler designs and low-temperature heat recovery systems for improved plant efficiencies, systems for improved ash disposability and reduced waste generation, and optimum system integration and plant controls. The technologies considered by these teams for low-emission boiler systems are discussed.