Heat Recovery Area Research Articles

Multi-factor coupling optimization of heat recovery effectiveness in a transcritical CO2 heat pump

In the background of energy shortage and climate change, transcritical CO2 heat pump(HTP) technology has attracted lots of attention because of its energy-saving and environmentally friendly advantages. In this research, an experimentally verified simulation model of transcritical CO2 HTP is established to investigate multi-factor coupling optimization of heat recovery effectiveness(ηIHX). First, the coupling optimization mechanism of ηIHX and discharge pressure(pdis) is analyzed. Moreover, this research explores the influence of ηIHX on heating capacity, power consumption, discharge temperature(tdis), and internal heat exchanger(IHX) cost, and further proposes a comprehensive heat recovery index to optimize the above factors. Based on this index the optimal heat recovery effectiveness(ηIHX,opt) for each operating condition is obtained. Also, a failure boundary for the coupling optimization of the ηIHX is also indicated. In addition, the optimal discharge pressure(pdis,opt) prediction correlation for different ηIHXs is proposed, which can be used for heat recovery effectiveness collaborative optimization control. Finally, a general method for evaluating IHX is provided. Taking Xi'an as an example, the optimal heat recovery area(AIHX,opt) of this HTP system is 0.42m2, with which the optimized HTP system operates safely at extreme operating conditions, resulting in an annual lucre of 1,211 CNY.

The effects of fractures on porous flow and heat transfer in a reservoir of a U-shaped closed geothermal system

In geothermal reservoirs, fractures, serving as preferential channels for heat transfer fluid circulation, can cause complicated migration patterns and heat transfer characteristics of the fluids. However, the crucial issue of whether and how fractures within a hydrothermal reservoir of a closed geothermal system (CGS) affect reservoir heat transfer fluid migration and the system’s heat transfer is still poorly understood. In this study, we construct a thermo-hydraulic coupling finite-element model to investigate the effects of fractures on fluid flow and heat transfer enhanced by natural convection in a U-shaped closed geothermal system (UCGS) with a horizontal well. We systematically analyze the responses of fluid migration and heat extraction in the system to key factors, such as fracture aperture, fracture azimuth, fracture distribution, and reservoir permeability. The results show that, in a high permeability reservoir (such as 2 × 10−13 m2), the fracture with an aperture of a millimeter scale can greatly strengthen and control the natural convection induced by heat transfer around the horizontal well in a UCGS, achieving a heat recovery efficiency of six times higher than conduction alone within the reservoir. The fracture azimuth can control the heat production region by guiding the evolution of natural convection. Intersecting network-distributed fractures can effectively improve heat recovery area and performance (more than 15%) compared to a single fracture. Some specific fracture segments within a fracture network may exhibit synergy or inhibition in different heat extraction stages, while a fracture connecting in the deep reservoir and orienting to the horizontal well may lead to heat breakthrough. In addition, a low-permeability interlayer below the horizontal well can restrict the heat recovery (nearly 20% drop in our models), but a fracture penetrating the layer can compensate for this hindrance. The findings of this study can contribute to understanding the thermodynamic mechanisms of fluid flow and heat transfer in a fractured reservoir, and then utilizing them to maximize heat recovery rather than considering conduction only, thus providing scientific insights into engineering practices of the UCGS.

Recovery of waste heat process through the various thermodynamic cycles: A critical review

This review study aimed at short description on most recent research available with regards to waste heat recovery (WHR) area which could be obtained with the help of various power as well as refrigeration cycles. From the literature, it is understood that WHR not only help us to reduce emission effects but even useful in energy saving that can further positively effect to the thermal performance or can be used for different purposes with the help of WHR cycles. Therefore, present study mainly discusses the literature with regard to application of various thermodynamic cycles widely employed these days for the WHR processes.

Degraded thermal stability of p-type Bi2Te3-based polycrystalline bulks for thermoelectric power generation at service temperature of 473 K

The Bi2Te3-based bulks are promising thermoelectric materials in the low temperature waste heat recovery area. However, their thermal stability needs to be addressed before they are applied in practical thermoelectric devices. In this work, the long-term thermal stabilities of the microstructure, thermoelectric properties and mechanical properties for the p-type Bi0.44Sb1.56Te3 polycrystalline bulks have been investigated at 423 and 473 K. The results indicated that the samples could keep the satisfying thermal stability when the service temperature was fixed at 423 K, and the grain size, the volume, the density and the thermoelectric properties of the samples remained almost unchanged during long term service, and the electrical transport properties were even improved with prolonging the servicing time to 168 h. However, when the service temperature was fixed at 473 K, the volume expansion was obvious with prolonging service time, and great quantity of voids were appeared in the bulks due to Te volatilization, which resulted in the obvious increase of the electrical resistivity and the deterioration of the electrical transport properties, and the unsatisfactory decrease of the power factor and the figure of merit. These results suggest that the long-term service temperature of p-type Bi2Te3-based polycrystalline bulks is only 423 K for the low-temperature thermoelectric power generation.

Technology competition in the internal combustion engine waste heat recovery: a patent landscape analysis

Fuel prices and tightening emission standards have challenged the dominance of internal combustion engines. As a response to this changed business context, the automotive industry has shown active interest in waste heat recovery technologies, which have seen rapid development in recent years. This paper uses a literature review and patent landscape analysis to study key emerging technologies in the field, namely, thermoelectric generators, and Rankine cycle and organic Rankine cycle systems. The state-of-the-art review highlights the challenges, advantages and future prospects of the selected technologies. The patent analysis reveals the leading countries, principal technological development indicators and most important actors active in the field. The results indicate a growing trend of patenting in all selected technologies. The United States and Japan are by far the most dominant countries in the waste heat recovery area, although their relative share of patent applications is declining. By applying a patent landscape approach, the study offers a quantitative perspective on current developments in waste heat recovery technology, provides indicators of future trends, and contributes to debate about technological competition in the automotive industry. Based on the conducted analyses, thermoelectric generators seems to be the most developed of the alternatives and closest to commercial application. Rankine cycle-based technologies, although less well developed, potentially offer greater environmental gains and better efficiency than thermoelectric generators. The study provides valuable information for stakeholders interested in waste heat recovery technologies and gives policymakers perspectives regarding different technological options in development of cleaner engine solutions.

Enrichment of thallium in fly ashes in a Spanish circulating fluidized-bed combustion plant

This work evaluates the behavior of thallium in a 50MW industrial circulating fluidized-bed combustion plant (CFBC), focusing on the distribution of this element among the bottom and fly ashes separated by the solid retention devices in the plant. The results show that thallium species are mainly retained in the solid by-products and are not emitted to air with flue gases in significant amounts, proving that this technology is a more effective means of preventing thallium emissions than pulverized coal combustion technology (PCC). The mass balance of the thallium content in the solids shows that this element was retained in the ashes separated by the different devices installed in the plant. An evaluation of the ash fractions taken from the strippers, the heat recovery area, the hoppers in the air heater and the electrostatic precipitator, shows that thallium was relatively homogeneously distributed in all the ash samples, independently of their composition, but is slightly related to surface area, which in turn is dependent on particle size and unburned carbon content.

Thermal fatigue and corrosion fatigue in heat recovery area wall side tubes

In this paper, findings of visual inspections, chemical analysis on deposits, metallurgical examinations and creep analysis on the failed SA210-A1 heat recovery area (HRA) wall side tubes of a boiler unit are presented. The investigations were carried out following two boiler tube failures at heat recovery areas involving the left hand side (LHS) and right hand side (RHS) side wall tubes. Findings from the microscopic examinations are used to support the investigation in determining the failure mechanisms. The first failure at LHS HRA side wall tube is identified due to thermal fatigue while the second failure is as a result of combination of the corrosion fatigue, thermal fatigue and creep damage. Recommendations are made to reduce unavailability of the boiler unit due to the HRA side wall tube failures.

97/02102 Influence of fuel type and steam cycle on CFB boiler configuration

The configuration of a circulating fluidized bed boiler is influenced by the fuel type that is to be burned and the specified steam cycle conditions. High quality fuels such as bituminous coal and petroleum coke have a high adiabatic flame temperature and require a significant amount of heat removal from the furnace solids circulation loop. Low quality, waste fuels such as anthracite culm and bituminous gob are just the opposite and require more heat removal from the heat recovery area (HRA). In one case additional heat transfer surface such as full height furnace walls, wing walls, and/or an external heat exchanger are required to maintain the desired furnace operating temperature. In the other case, steam generating heat transfer surface or a steaming economizer may be required in the HRA to generate the required amount of steam. Also, economizer coils may be required in the bottom ash coolers to adequately cool large quantities of ash. Steam cycle conditions such as unit capacity, final steam temperature and pressure, feedwater temperature, and whether reheat is required also dictate how a unit will be configured. Small capacity units have a small furnace cross sectional area. enclosure heat transfer surface is therefore large compared tomore » the volume of gas and solids within the furnace. Large capacity units are just the opposite and may require internal heat transfer surface or an external heat exchanger to maintain the desired furnace operating temperature. High temperature reheat steam cycles require some reheat or superheat duty to be accomplished in the furnace solids circulation loop. Low temperature and pressure, non-reheat units may require little or no superheat, in which case a water-cooled may be preferred over a steam-cooled cyclone. Described in this paper is how these and other issues are addressed when designing a CFB boiler.« less

Process and layout design of a combined MSF/VTE plant

The combination of multi-stage flash evaporation (MSF) and multiple effect evaporation (ME) unites the advantages of improved heat transfer with the more favourable heat transfer conditions in the MSF part at lower temperatures. In comparison with conventional MSF or ME processes the specific energy requirement can be significantly reduced. Moreover, structural integration of both MSF and ME stages in a combined MSF/VTE evaporator would seem obvious, since evaporator trains of large capacity can be built-up by serial connection. The combined MSF/VTE process is established by the parallel connection of a MSF once-through plant with a ME unit. The brine is first pre- heated in the heat recovery area of the MSF part, is conveyed through the brine heater and then flashed in the MSF stages. In certain MSF stages, part of the brine is recycled to the VTE part of the plant where it evaporates inside. The vapor arising in one VTE evaporator is used as steam in the next following VTE effect. The condensate and the thickened brine is re-fed into the discharge stage of the MSF train. Heat input into the MSF part is effected by a separate brine heater, and into the VTE part directly in the first VTE evaporator of the plant. The heat rejection area is located in the MSF part and is operated in the usual way. The vapor from the last VTE effect is condensed in a final condenser. In the special case of a multi-purpose plant with a capacity of 5 MIGD, where the maximum process temperature has been fixed at 180°C because scale forming substances have been removed by preceding water treatment, the complete plant comprises 20 combined MSF/VTE modules in the heat recovery area and two MSF stages in the heat rejection area. One MSF/VTE modules consists of two MSF stages and one VTE evaporator. The concentration ratio of the brine is C V = 5. Extended thermohydraulic evaluations and heat transfer calculations show that this plant configuration yields a performance ratio of PR = 15.