Cascade Utilization Of Heat Research Articles

Computational boundary improvement and performance optimization of the flue gas waste heat cascade utilization system of the ultra-supercritical 1000 MW generator set

Abstract There is no uniform performance test rule and standard calculation method for efficiency improvement of a system that utilizes waste heat from flue gas and it is mainly carried out through turbine parameters, without considering boiler system performance. Given the above problem, in this paper, the steam turbine, boiler and waste heat from the flue gas step-up utilization system are calculated by establishing a thermal model of ultra-supercritical secondary reheating 1000 MW unit. At the same time, unit design data and field performance test results are used for verification. Analysis comparing simulation outcomes with experimental data revealed that the discrepancies in the heat consumption rate per unit, the efficiency of the boiler, and the rate of coal consumption for power generation peaked at a marginal variance of 0.2%. The optimum operating parameters of the system for low-grade flue gas recovery in a cascading manner are obtained through variable operating condition calculations. The optimum value of high-pressure bypass feed-water flow rate is 52 kg/s at 970 MW operating condition. At the same time, the difference between high-pressure bypass effluent and high plus effluent temperatures should be controlled to be close to 0°C, and the optimal value of low-pressure bypass condensate flow rate is 53 kg/s. As the flow of flue gas in the bypass increases, the efficiency of heat exchange in the bypass economizer also increases, resulting in greater absorption of heat in the utilization apparatus for flue gas waste heat, leading to a more effective energy-saving outcome. However, it is necessary to regulate the temperature of both the primary and secondary air to levels that exceed the minimum requirements for the safe functioning of the coal mill.

Exergoeconomic Evaluation of a Cogeneration System Driven by a Natural Gas and Biomass Co-Firing Gas Turbine Combined with a Steam Rankine Cycle, Organic Rankine Cycle, and Absorption Chiller

Considering energy conversion efficiency, pollution emissions, and economic benefits, combining biomass with fossil fuels in power generation facilities is a viable approach to address prevailing energy deficits and environmental challenges. This research aimed to investigate the thermodynamic and exergoeconomic performance of a novel power and cooling cogeneration system based on a natural gas–biomass dual fuel gas turbine (DFGT). In this system, a steam Rankine cycle (SRC), a single-effect absorption chiller (SEAC), and an organic Rankine cycle (ORC) are employed as bottoming cycles for the waste heat cascade utilization of the DFGT. The effects of main operating parameters on the performance criteria are examined, and multi-objective optimization is accomplished with a genetic algorithm using exergy efficiency and the sum unit cost of the product (SUCP) as the objective functions. The results demonstrate the higher energy utilization efficiency of the proposed system with the thermal and exergy efficiencies of 75.69% and 41.76%, respectively, while the SUCP is 13.37 $/GJ. The exergy analysis reveals that the combustion chamber takes the largest proportion of the exergy destruction rate. The parametric analysis shows that the thermal and exergy efficiencies, as well as the SUCP, rise with the increase in the gas turbine inlet temperature or with the decrease in the preheated air temperature. Higher exergy efficiency and lower SUCP could be obtained by increasing the SRC turbine inlet pressure or decreasing the SRC condensation temperature. Finally, optimization results indicate that the system with an optimum solution yields 0.3% higher exergy efficiency and 2.8% lower SUCP compared with the base case.

Experimental and simulation study on an air conditioning system cascade driven by waste heat using multicomponent solution

The cascade utilization of waste heat for air conditioning system is still considerably lacking in the literature, especially for waste heat below 80.0 °C. In this paper, the experimental and simulation studies are carried out on an air conditioning system that integrates the absorption refrigeration subsystem (ARS) with the liquid desiccant dehumidification subsystem (LDDS). The waste heat at 80 °C is first used to drive the ARS to produce chilled water for air cooling, and then drive the LDDS for air dehumidification to realize heat cascade utilization. Firstly, the experimental study is conducted to compare CaBr2–LiCl–H2O with LiBr–H2O in the ARS and CaBr2–CaCl2–H2O with LiCl–H2O in the LDDS. The results show that the multicomponent solutions perform comparably to the single-component solutions. Then, a mathematical model is established to simulate the entire system using the appropriate multicomponent solution for each subsystem. It is found that the COP of the system reaches 0.77 at a driving temperature of 80.0 °C, with the supply air temperature of 23.0 °C and the humidity ratio of 10.5 g/kg. The waste heat can be recovered down to 61.0 °C, achieving a heat recovery depth of 19.0 °C. This system is expected to have significant potential in the applications due to its efficient heat utilization capability and low-cost multicomponent solutions.

Thermodynamic analysis of a hybrid energy system coupling solar organic Rankine cycle and ground source heat pump: Exploring heat cascade utilization

The demand for efficient utilization of renewable energy is growing and the hybrid energy system driven by solar and geothermal energy is a significant way to achieve carbon neutrality. This paper presents a hybrid energy system coupling solar organic Rankine cycle (S-ORC) with ground source heat pump (GSHP) for heating and power supply to explore the heat cascade utilization. In the hybrid energy system, the ground heat exchanger (GHE) is shared by the S-ORC and GSHP systems and the waste heat from the condenser of S-ORC is recovered to enhance the coefficient of performance (COP) of GSHP. A mathematical model is optimized to analyze the parametric effects on thermodynamic performance. The results indicate that the COP of the hybrid energy system can be improved up to 6.5 which shows the obvious advantage compared to 2.8 of the stand-alone GSHP system. Furthermore, the hybrid energy system can obtain optimum exergy efficiency by matching ground source temperature and condensation temperature in the ORC unit. For a building of 3000 m2 with heating and power supply, multi-objective optimization is carried out to obtain the optimal design performance that the net power output, thermal efficiency and exergy efficiency are 180.0 kW, 27.5%, and 9.2% respectively.

Thermal economy analysis of flue gas waste heat utilization system of 1000MW secondary reheat unit

Deep utilization of flue gas waste heat is an important means to ameliorate the power generation productivity of coal-fired units. Aiming at the waste heat cascade utilization system which is composed of “air preheater bypass + two-stage low-temperature coal economizer + thermal primary air temperature regulating device” proposed in a certain project, using the energy balance method and the equivalent enthalpy drop method, the mathematical model of the impact of waste heat utilization devices at all levels on the unit economy is established from the boiler efficiency and steam engine heat rate. Combined with the rated operation data of the unit, the thermal economy of the system is analyzed. The results show that the bypass of the air preheater and the temperature regulating device of the hot primary air can effectively improve the utilization efficiency of the waste heat of the flue gas at the tail of the boiler, the coal consumption of power supply can be reduced by 3.47 g/kWh under rated working conditions.

Thermo-economic evaluation and optimization of solar-driven power-to-chemical systems with thermal, electricity, and chemical storage

This paper evaluates the thermo-economics of power-to-chemicals using solar energy, with the chemicals being methane, methanol, and gasoline. In addition to the optimal technology sizing and heat cascade utilization, this paper also considers the optimal molten-salt solar power tower (MSPT) design, as the MSPT significantly affects the levelized product cost. A bi-level optimization is proposed, employing mixed-integer linear programming at the lower level with heat and mass integration for optimizing sizes and operating strategies of technologies, and with heat cascade utilization and a genetic algorithm at the upper level for optimizing the MSPT design. In the upper level, the full-load storage hours, design direct normal irradiance, solar multiple, and sizes of the MSPT are optimized. The electricity sources considered are the MSPT, photovoltaic (PV) with daily electricity storage, and the electrical grid as a complementary technology to satisfy the targeted daily product demand. Cost-competitiveness of solar-driven chemical synthesis is thoroughly assessed via considering sensitivity analysis on 1) regional solar resource endowments and actual local demands; 2) electricity sources, that is, PV vs. MSPT; and 3) the scale effect represented by different chemicals’ yield. The results show that the levelized methane cost ranges from 4.5 to 8.5 €/kg, depending on the location, plant size, and annual power contribution of concentrated solar power. Due to the larger mass production, the levelized cost of methanol and gasoline is lower: 1.5–2.2 €/kg for methanol and 4–6 €/kg for gasoline. The findings highlight the significance of location choice, that is, natural endowment of solar radiation and carbon sources. Using the syngas co-electrolysis pathway and direct solar radiation 100 kWh/m2 higher, the methane production cost is decreased by 2.4 €/kg. Sensitivity analysis performed on plant scale reveals that a compact, small-scale system is far too expensive. The levelized cost of methane could be decreased by 1.2 €/kg when the plant is scaled up from 4,000 to 20,000 kg/day H2. Due to its expensive electricity storage and limited working hours, PV is typically not chosen as a power source. Overall, solar fuels are unlikely to be cost-competitive in the near future when compared to market prices for all three compounds under consideration.

An optical concentrator coupled multistage solar steam generation system for solar thermal-latent heat cascade utilization and water desalination: Performance and economic benefit analysis

Solar steam generation (SSG) for water treatment has attracted great interest for its convenience, accessibility and eco-friendliness. However, water production rate of traditional floating structure SSG system is relatively low. To further increase the water production rate, we develop a solar thermal-latent heat cascade utilization SSG system coupled with compound parabolic concentrator for desalination. A 2 × compound parabolic concentrator (CPC) was used in the outdoor experiment to improve the incident solar flux. Solar absorber of the SSG module has a high solar absorbance of 95 % which can effectively harvest solar energy and convert it into heat. A thin air gap above the solar absorber can restrain thermal loss through convection and radiation. Within the SSG module, seawater was supplied for the evaporation process driven by the capillary force in the capillary wick. Through the multi-stage design, solar thermal conversion and latent heat cascade recovery were achieved. As a result, the SSG module can achieve a gain to output ratio (GOR) of 185.09 % with a water flux of 2.82 kg∙m−2∙h−1 under one sun. Concentrating solar flux reached 1300 W∙m−2 in an early autumn day and a corresponding water flux of 3.5 kg∙m−2∙h−1 was achieved. Theoretical analysis showed that higher solar flux can increase the GOR. Optical concentration of 2 × can increase annual fresh water by 1.72 times while maintaining economic benefit. An insulation air gap above the solar absorber can reduce thermal loss from the solar absorber. Increasing stages can increase number of times the latent heat being reused and improve GOR, but economic benefit decreased with the increase of stage number. Considering the economic benefit and floor area, optical stage number of the system should be 4. Annual water production evaluation showed that a 1 m2 area system can annually generate 6321.29 kg fresh water with a water production cost of 7.03$/m3.

Influence study of bottom cycle ratios and superheat for vessels waste heat cascade recovery based on TEG-ORC combined cycle system employing R245fa

ABSTRACT The vessel’s waste heat has the characteristics of a large temperature gradient, huge recoverable volumes, and various properties. TEG-ORC combined cycle is a promising method for multiple vessels waste heat cascade utilization. Keeping the evaporation pressure at 0.7Mpa, R245fa of low toxicity and environmental friendly is employed for the research under the conditions of different bottom cycle ratios(₣) and superheating. The interaction between essential parameters and system performance is explored. As the ₣ gets larger, the system net power output (W net ), the system thermal efficiency (η s ) and the waste heat utilization of main engine flue gas (f g ) gradually increase, the power-production cost (C g ) of the system gradually decreases. When the degree of superheat increases from 3.36K to 9.23K, the output power of the expander increases synchronously. The results show that superheating improves the combined cycle W net and f g while reducing theC g . The stability and safety of the ORC unit are further enhanced by expanding the ₣. When the ₣ is 0.885 and superheat is 11.28 K, W net is 965.18 W, η s is 8.74%, and the C g of the system is 0.5363 $ k Wh−1, and the rate of f g is 85.07%.

Performance investigation and collaborative optimization of power, economy and NOx removal for waste heat cascade utilization system in ocean-going vessels

Waste heat recovery technology of ships is meaningful for the enhancement of system efficiency and protection of environment. Compared with conventional diesel engines, the natural gas engines have the advantage of low emission, and its exhaust gas with quite high temperature is very suitable for utilization as the heat source of cascade waste heat system. This study integrates an over-expansion transcritical CO2 cycle with a double effect absorption refrigeration cycle to recover the heat energy from a natural gas engine. At the same time, a post-processing unit is proposed to remove the nitrogen oxide of flue gas. The research results indicate that the higher engine load contributes to improving the equivalent output work and economy of the combined cycle while the post-processing unit can further reduce the payback time under the given conditions. In terms of the parameters analyses, the turbine outlet pressure of transcritical cycle has an optimal value of 2.25 MPa, which can make the output work to reach the maximum value of 305.0 kW, and the performance improvement of refrigeration cycle can be achieved by decreasing the temperature of high pressure generator or increasing the temperature of low pressure generator. After multi-objective optimization, the residual equivalent output work, payback period and amount of NOx reduction of the total system are 150.77 kW, 4.20 years and 8.16 g/kWh, respectively. In addition, the Energy Efficiency Existing Ship Index is further reduced to 8.21 gCO2/ton·nm with the aid of the proposed system.

Cascade utilization of low-grade thermal energy by coupled elastocaloric power and cooling cycle

Unlike the conventional elastocaloric cooling system that depends on electricity, the coupled elastocaloric power and cooling cycle proposed in this study exploits low-grade thermal energy in a cascade manner, which opens a new paradigm for the caloric cooling community. Cascade utilization of heat relies on a gradient of transition temperature inside the shape memory alloy actuator that best matches the temperature profile of the material during operation. A transient numerical model is developed to simulate the performance of this new system, and the model is experimentally validated. The transition temperature gradient should exceed 60 K for optimum utilization of input heat. At the same gradient, the distribution of transition temperature can be optimized, where at least 10% improvement over linear profile can be expected in terms of efficiency and cooling power density. Based on the superior performance, this technology could be powered by solar thermal collectors working at 110 °C and could be applied to residential air-conditioners and off-grid refrigerators. The novel system proposed in this study not only complements the existing library of heat-activated cooling technologies, but also provides a new pathway for the expansion of caloric cooling at large.

Combined microgrid power production and carbon dioxide capture by waste heat cascade utilization of the solar driven Organic Rankine cycle

This paper proposes to utilize the waste heat of a solar-driven Organic Rankine cycle (ORC) to support the regeneration process of the carbon capture by adsorption (CCA) subsystem. The waste heat is utilized in cascaded form, where the higher temperature component is supplied to the CCA device, and the lower temperature component is internally exchanged to increase the ORC efficiency. The proposed system is studied for the microgrid application, where a thermodynamic analysis is conducted to evaluate the electrical and exergy performance of the proposed system under 1 day of solar irradiance. The analysis is achieved by coupling the simulation models of each subsystem, where the influences of the ORC pressure ratio, turbine inlet temperature, regeneration temperature, and the CO2 input source are investigated. Results show that the proposed system is optimal when combined with CO2 capture of the animal farm; When a 50 m2 and 100 solar concentrations solar thermal plant is used, an optimal regeneration temperature of 75 °C existed to yield 4375.6 kg of CO2 per day and 0.3 MW electricity. The corresponding ORC and CO2 capture exergy efficiencies are 0.25 and 0.012, respectively, which sum to be higher than the basic solar-ORC under the same conditions.

Analysis and Evaluation of Multi-Energy Cascade Utilization System for Ultra-Supercritical Units

To address the large temperature difference in the air heater (AH) inlet of a traditional exhaust heat utilization system and energy grade mismatch problems during the heat and mass transfer processes, this study proposed a new multi-level waste heat cascade utilization system. Based on a principle of “temperature-to-port and cascade utilization”, this system uses the boiler side high-temperature flue gas and low-temperature air, and the turbine side high-temperature feed water and low-temperature condensate water, to conduct cross heat exchange according to the energy grade matching principle. Combined with a typical 1000 MW coal-fired unit, the heat transfer characteristics and energy-saving benefits of the new system were analyzed. The results showed that the new system has excellent performance: the heat rate decreased by 91 kJ/kWh, coal consumption decreased by 3.3 g/kWh, and power generation efficiency increased to 49.39%.

A novel solar-assisted ground-source heat pump (SAGSHP) with seasonal heat-storage and heat cascade utilization: Field test and performance analysis

To maintain the energy quality with high temperature and reduce the energy loss of seasonal heat-storage in solar-assisted ground-source heat pumps (SAGSHPs), a novel SAGSHP system with the heat-cascading of borehole heat-exchangers was designed and its field-test was conducted in this paper. The borehole heat-exchangers were divided into two regions: the core region and the peripheral region. The core region can maintain a high temperature (e.g. 45 °C), which is much higher than in previous studies, and the heat from this region can be used directly, without the operation of a heat pump. A field-test was conducted in a community in the province Shandong, China. The results indicate that a sufficient soil-temperature gradient (the temperature is high in the core but low at the periphery) can be created and maintained. The monthly averaged borehole-wall-temperature difference between the borehole heat-exchangers (BHEs) at the core and the periphery can be as high as 30.1 °C. This means that both cascaded heat-storage and heat-utilization can be realized. In addition, an average performance of CCOP = 5.15 and SCOP = 4.66 can be achieved. Compared with previous studies, despite the lower CCOP, a higher SCOP can be attained, thanks to heat cascade storage and -utilization. The novel approach described in this paper represents a viable alternative for space heating in North China.

The analysis and research on variable operating condition of exhaust steam and waste heat Cascade utilization system of air cooling heating unit

The series and parallel exhaust heat cascade utilization system was adopted by the large direct air cooling heating units. On the one hand, this system could reduce the adverse impact on power generation; on the other hand, it could reduce the temperature difference of heat transfer through step by step heating, the irreversible loss could be reduced, and the energy utilization efficiency could be made higher. On the basis of grasping the design performance of exhaust steam utilization system and the variable operating performance of main equipment by analysing the data of typical operating conditions, the optimization analysis model of heat pump group and the whole plant was established by this paper. The performance of heat pump unit under variable operating conditions was analysed and calculated, the influence of different exhaust pressure and backwater temperature on the economy of the whole machine was analysed, and the optimal operation mode of the heat pump was obtained. Finally, the pumping and condensing ratio curves under different conditions of winter heating conditions were determined, which could guide the optimal operation of heat pump units. It also provided technical support and basis for deep peak regulation or flexible transformation of heating units.

Investigation of a cascade waste heat recovery system based on coupling of steam Rankine cycle and NH3-H2O absorption refrigeration cycle

Cogeneration system based on cascade utilization of heat has been proved to be a promising technology to enhance energy conversion efficiency. An electricity-cooling cogeneration system (ECCS) based on coupling of a steam Rankine cycle (SRC) and an absorption refrigeration system (ARS) is proposed to recover the waste heat of marine engine to meet the electricity and cooling demand aboard. The SRC absorbed heat from the exhaust gas of engine to generate electricity, and the ARS makes use of the condensation heat of SRC to provide cooling needed on ship. Electricity output, cooling capacity, equivalent electricity output, exergy efficiency, and equivalent thermal efficiency are adopted to evaluate the performance of ECCS. The simulation results indicate that recovering the expansion work in the absorption refrigeration cycle is an effective way to increase electricity output at the cost of decreasing cooling capacity. The equivalent electricity output of the WHR system is 5223 kW, accounting for 7.61% of the rated power output of the marine engine.

The feasibility analysis for the concept of low temperature district heating network with cascade utilization of heat between networks

Recently, low temperature district heating networks (LTDH) have received attention in district heating and cooling market due to their benefits in terms of efficiency, greenhouse gas reduction, flexibility to use renewable energy sources and economic benefits. In this work, physical and techno-economical aspects of the new concept of cascade types with high temperature district heating (HTDH) return is utilized to supply heat at low temperature networks. The HTDH return water temperature is around 45oC and supply of LTDH can be set around 60oC. The return water temperature of HTDH return line at 45oC can be raised to 60oC with the help of heat pump. A detailed study of major components, network design, pressure drop, heat loss and power consumption was performed to formulate an annual, hourly, based energy simulation to assess the techno-economic feasibility of the systems for different types of customers (residential & commercial) The economics were also analysed in terms of internal rate of return (IRR) and the results show that IRR for residential buildings varies from 14 ~ 17%. In order for the successful realization of the proposed system in the market new sustainable systems encouragement in government level is desired to be provided in the form of renewable energy target/certificates or CO2 reduction incentives especially at the initial stage of the commercialization of the model.

Energy and exergy analysis for waste heat cascade utilization in sinter cooling bed

In the present paper, a numerical study is presented to investigate the cascade utilization of waste heat in sinter cooling bed. With the aid of CFD (computational fluid dynamics), a two-dimensional unsteady mathematical model, which would significantly reduce the computational time, is established to describe three-dimensional steady flow and heat transfer in sinter cooling bed. The Brinkman–Forchheimer extended Darcy model and the LTNE (local thermal non-equilibrium) model are employed to describe flow and heat transfer in sinter cooling bed. And the reliability of this mathematical model is validated with both related simulation and experimental work. And then, numerical simulations are conducted to examine the effects of different operating parameters on the cooling air temperature and waste heat utilization quantity. Furthermore, the waste heat grade and quantity are taken into comprehensive consideration in energy and exergy analysis. The results indicate that, both the quantity and quality of waste heat utilization would be improved by increasing sinter cooling bed height, trolly's moving speed and sinter heat flux. Meanwhile, it is also found that, with different assignments of cooling air flow rate, the quantity and quality of waste heat in sinter cooling bed would not be improved at the same time.

Thermodynamic Analysis of Thermochemical Recovery of High Temperature Wastes.

This paper describes a feasibility study of direct heat recovery system from high temperature wastes over 1 700 K by using objective chemical reaction, in which enthalpy-exergy diagram, so-called thermodynamic compass, is introduced for evaluating various systems. Blast furnace slag was taken as an example for the evaluation and familiar endothermic reactions in the cement production, the chemical industry, etc. were selected as a combination process for the heat recovery. Exergy analysis of cement and methanol plants was also carried out for further discussion. The results showed that decomposition of limestone, reforming of methane and gasification of carbon are the most promising for heat recovery of the high temperature wastes; various slag and LD gas, from a viewpoint of effective use of exergy, not energy. This also appeals a possibility of next generation symbiotic steelworks with heat cascade utilization, rather than heat recovery.