Low Temperature Process Heat Research Articles

Energy-efficient production of sustainable industrial process heat with a parabolic dish-conical cavity solar collector

Industrial decarbonization in response to global carbon neutrality requires vast process heat to be supplied in a low-carbon manner. Solar energy is regarded as one of the most promising alternatives to fossil fuel applied for heat-driven industrial processes, however, lack of effective approaches to improve the solar-thermal conversion efficiency is a longstanding issue. Here, we propose an efficient approach to produce industrial process heat based on a novel concentrated solar collector, mainly consisting of a parabolic dish concentrator and a conical cavity receiver. Results showed that the collector was competent to supply the process heat meeting various low-temperature industrial occasions, and there was an optimum flow rate to achieve a trade-off between the outlet temperature of working fluid and thermal efficiency of the solar collector. The thermal efficiency of the proposed solar collector was 2.7%–27.5% higher than that of most other existing collectors used for production of low-temperature process heat, and such a superior solar-thermal conversion efficiency was a consequence of the reduction in energy losses between the solar receiver and surroundings as confirmed by the comprehensive energy analysis performed in this study.

Nuclear microreactors: Status review and potential applications; the Mexican case

Microreactors are a class of small modular reactor with a typical power output up to 10 MWe. Their factory fabricated, transportable, and self-regulating design makes the microreactors suitable for supplying electricity to off-grid communities, emergency situations, and space and naval applications. Likewise, microreactors are appropriate for non-power applications such as hydrogen and synthetic fuels production, high and low temperature process heat, various industries (mining, cement, etc.), district heating, and water desalination. Many microreactor concepts are under development around the world with different nuclear technologies, such as the Micro Modular Reactor, a high temperature gas-cooled reactor; Aurora, a liquid metal-cooled fast reactor; and eVinci, a heat pipe-cooled reactor, among others. A recent market assessment of microreactors, conducted by the Idaho National Laboratory, identifies five potential markets for microreactors: Isolated Operations, Distributed Energy, Resilient Urban, Disaster Relief, and Marine Propulsion. In the case of Mexico, which remains dependent on fossil fuels for its energy supply (oil covers 44% of the energy source, while natural gas covers 38% and coal 3%), all potential markets are attractive to consider deploying microreactors, particularly Isolated Operations and Distributed Energy, due to its industrial sector and remote/isolated communities. Mexico’s mining cement, and iron and steel industries are the major consumers of electricity, which is generated primarily with fossil fuels. Similarly, oil accounts for 99.7% of the energy mix of the national transport sector. Furthermore, isolated regions in Mexico, such as the state of Baja California Sur, which generates its own electricity mainly with natural gas, fuel oil, and diesel, could implement microreactors, not only as a potential solution for their electricity supply, but also to implement cogeneration application as water desalination.

Life cycle greenhouse gas emissions of low-temperature process heat generation by external compound parabolic concentrator (XCPC) solar thermal array

New solar-based technologies are currently being developed as prospective low-carbon sources of heat for industry, which require life cycle assessment to determine their actual decarbonization potential relative to current heat sources. We performed the first life cycle assessment of the external compound parabolic concentrator (XCPC) solar array, a novel low-concentration and non-tracking solar thermal technology capable of providing low-to medium-temperature heat (up to 250 °C). Primary data on the materials and performance of the XCPC were used in this analysis. The embodied greenhouse gas (GHG) emissions associated with manufacturing the technology are 92.4 kg CO2eq/m2, cradle-to-gate. The life cycle GHG emissions cradle-to-grave over a 25-year lifetime under conditions in the Central Valley of California are 129.7 kg CO2eq/m2. On the basis of thermal energy delivered, the XCPC has a carbon footprint of 5.8 g CO2eq per kWhth. These results indicate that the XCPC can generate low temperature heat with a carbon footprint 97% lower than natural gas and 98% lower than propane combustion in regions of high solar insolation.

Experimental evaluation of a thermosyphon-based waste-heat recovery and reintegration device: A case study on low-temperature process heat from a microbrewery plant

An experimental study was conducted to design, build and test the performance of a waste-heat recovery device. Its feasibility and performance were evaluated, based on its implementation within a brewing process; recovering unallocated residual energy from wort cooling water (40 °C to 80 °C) and using it to heat cool air for barley drying (32 °C to 48 °C). Given the quality associated to the low-temperature source, thermosyphons were selected as heat conveyance device. The proposed heat recuperator design uses 18 carbon-steel thermosyphon tubes filled with a mixture of distilled water and hydrazine hydrate, as corrosion inhibitor, at 20% of the total inner volume. Given the passive nature of the device, the length ratio between the evaporation and condensation zones was also analysed, ranging from 50:50, 40:60 and 30:70. The results showed that the 50:50 length ratio was the most disadvantageous configuration available, with the lowest efficiency and heat conveyance, ascribed to a higher radial heat flux into the evaporator, thus, reducing the operation range considerably. Meanwhile, increasing condenser length, 40:60 and 30:70 length ratios, yields a higher maximum condensation heat flow, with 4.15 KW and 4.22 KW, respectively, a 31% increase. However, given the 1.2% difference between them, said increase is comparatively negligible, entailing that, for this thermosyphon setup, peak heat transfer available is reached with the 40:60 length ratio. Regarding efficiencies, it was found that the 50:50 length ratio is particularly susceptible to the thermosyphon inherent operation limits, specifically, the boiling limit. Nonetheless, all configurations have efficiencies above 50% with heat flows above 1.5 KW. Additionally, it was found that the lowest air flow velocities yield the highest achievable efficiencies, with 84%, 98% and 94%, for the 50:50, 40:60 and 30:70 length ratios respectively. Similarly, when evaluating through the thermal capacity framework, it was found that the 50:50 length ratio only possess a 8% accomplishment rate, whilst the remaining configurations, increase said rate by 20%. However, it also shows that the 30:70 length ratio yields a more dispersed dataset, which reveals that the imbalance after surpassing peak heat transfer, renders the device more susceptible to both inherent and environmental effects. From the findings it was found that the proposed device, with a 40:60 length ratio is capable of successful recover and reintegration of residual energy, without modifying existing brewhouse installation or requiring additional energy input. Therefore, the general assessment conducted proposes thermosyphon-based heat exchangers as viable alternatives for low-temperature heat recuperation beyond the case study here discussed.

Robust Design Approach for Low-Temperature Solar Thermal Utility Systems

This work looks at the design of flat-plate solar collector utility systems for the supply of low-temperature process heat, subject to restrictions such as the availability of land area for installation. The design approach is based on the formulation of a multi-objective optimisation strategy. The main stages in the methodology are (a) the use of a parametric model that predicts the thermohydraulic performance of a network of solar collectors and (b) a two-level multi-objective optimisation approach where the collector geometry is first optimised followed by the optimisation of the design of the network structure. The application of the proposed methodology to a case study reveals that the approach produces designs that are capable of efficiently operating throughout the year delivering the required process thermal needs. The results show that optimised designs exhibit a payback time reduction of 55.5% with respect to a design using standard commercial collectors.

Numerical optimization and convective thermal loss analysis of improved solar parabolic trough collector receiver system with one sided thermal insulation

Two type of receiver systems currently employed in solar parabolic trough collector technology are evacuated annuli receivers and air filled annuli receivers. While former receiver finds its way into high-temperature grid-acquaintance solar parabolic trough collectors, latter are more inclined towards non-grid solar thermal applications like low-temperature process heat. Evacuated receivers utilize vacuum filled annuli to reduce down the convection losses; this makes them substantially expensive – while prizing them as benchmark among receivers. Contrary, air filled annuli based receivers are relatively less expensive but are sub-par in thermal performance relative to evacuated receivers. This work deals with the air filled receiver system and would try to abridge the economy and efficiency between both types of systems using computational fluid dynamics (CFD) based numerical simulation approach. A heat blocking thermal insulation was tailored and fitted in the sun facing receiver annulus which does not receive concentrated radiation of the Sun, and was simulated for the reduction in convective losses and for favourable circumferential temperature distribution (CTD) around the absorber. Consequently, its convective heat losses were investigated for varying wind speeds and mass flow rates of heat transfer fluid (HTF) and were compared with mainstream air filled annuli receivers. Simulation results are compared with experimentation in which wind velocity was in a range of 0.43–4.99m/s. It has been found that glass envelope temperature decreases with increase in wind velocity which directly insinuates the decrease in convection losses around glass envelope. These comparative implications could be served as a point of reference to develop solar parabolic trough collector for small scale process heat applications in India.

Optimization of Heat Exchanger Networks for the Utilization of Low-Temperature Process Heat

A heat exchanger network (HEN), using water as a circulating medium, can recover heat from hot process streams and transfer it to cold process streams. Design optimization of such an HEN for utilization of low-temperature process heat (LTHEN) is a complex task. In this paper, three mixed-integer nonlinear programming models, namely, synthesis, retrofit, and alternate retrofit models are formulated to minimize the total annual cost (TAC), for realistic LTHEN design by considering pressure drops and costs of piping, water tanks, pumps, and heat exchangers. The synthesis model provides the best LTHEN design for complete heat recovery from hot process streams and supplying it to cold process streams via the circulating water stream. The retrofit model considers heat recovery from hot process streams to cold process streams only if it is economical by considering trade-off between the capital cost of new heat exchangers and utility cost of existing heaters/coolers. Finally, the alternate retrofit model is similar to the retrofit model except that the former considers heat exchanger costs for heat exchange between hot/cold process streams and cold/hot utilities. One detailed case study from a petroleum refinery is presented to demonstrate the potential benefits of using the proposed models, which provide realistic and industrially acceptable LTHEN design. Use of multiple LTHEN circuits is considered, and the result is compared with the single circuit solution.

CCS Feasibility Improvement in Industrial and Municipal Applications by Heat Utilisation

This paper describes implications of applying carbon capture and storage in combined heat and power (CHP) production and in steel industry through three case study approaches conducted in Finland. Utilisation of low temperature process heat from capture plant, air separation unit or CO2 compression in district heating system and/or industrial solutions offers significant potential to increase overall efficiency and feasibility of CCS processes. The effects of CCS on the local CHP systems were included within the studied system boundaries in order to evaluate the economics and emissions from investor's (local energy company) point of view. Effect of CCS on greenhouse gas (GHG) emissions and operation economics of the CCS cases are compared to the reference system with varying parameters of operation. Regarding the GHG emissions, besides the site emissions, the main effects on global GHG emissions are also taken into account by using system modeling and streamlined LCA.In the case studies the whole CCS chain, including CO2 capture, processing, transport and storage, was included. Carbon capture processes were modeled using Aspen Plus and Prosim process modeling software and the results were used in CCS plant economics toolkit (CC-Skynet™) to estimate CO2 emission reduction possibilities and carbon abatement costs. Studied case studies included three main applications which were studied in different operational situations. The properties of reference plants and CHP systems are based on the real operational CHP units and steel mill in Finland.The first presented application is retrofit of about 1000 MWfuel CHP plant with post combustion capture technology. Natural gas fired GTCC plant is part of relatively large district heating network including also other CHP units in the same network. The plant is situated on the coastal area of Southern Finland and it emits approximately 1.3 Mtn CO2/year.The second application is a greenfield about 500 MWfuel CHP plant situated on the coast of the Gulf of Bothnia and emitting approximately 1.5 Mtn CO2/year. The plant is based on a modern CFB-boiler which is equipped with oxy- fuel technology in the CCS case. The studied fuel-shares with and without CCS consisted of pure biomass, pure peat and biomass-peat co-firing. In the study it is assumed that the economic incentive for negative CO2 emission is included in EU ETS for Bio-CCS. The plant is connected to the existing district heating network where older CHP plant already exists. Another plant and limited district heat consumption in the area limits the benefits obtained from CCS heat recovery.The third application is an integrated steel mill situated on the coast of the Gulf of Bothnia and emitting approximately 4.0 Mtn CO2/year altogether. The mill is retrofitted for post combustion capture and implications of different capture amounts, different solvents and process integration levels are compared to the base case steel production with varying operational parameters. Process heat is utilized also as district heat but heat consumption in the district heat network is smaller than the amount of recoverable process heat in the mill.The results showed that significant improvements can be achieved by CHP in plants utilizing CCS, especially in the case of oxy-fuel. The feasibility of CCS is heavily dependent not only on the characteristics of the facility and the operational environment but also on the chosen system boundaries and assumptions. In combined heat and power plants, major improvements can be obtained with heat integration, especially, in the production of district heat. In the near future particularly large, new and flexible CHP plants, which can burn coal, biomass or peat, are seen as promising candidates for CCS in Finland.

VHTR-based systems for autonomous co-generation applications

As highly efficient advanced nuclear systems, Generation IV Very High Temperature Reactors (VHTR) can be considered in a variety of configurations for electricity generation and process heat applications. Simultaneous delivery of electricity, low-temperature process heat (for potable water production, district heating, etc.) and high temperature process heat (for hydrogen production, etc.) by a single cogeneration system offers unique deployment options as “all-in-one” power stations. This paper is focused on the VHTR-based systems for autonomous co-generation applications. The analysis is being performed within the scope of the U.S. DOE NERI project on utilization of higher actinides (TRUs and partitioned MAs) as a fuel component for extended-life VHTR configurations. It accounts for system performance characteristics including VHTR physics features, control options and energy conversion efficiencies. Utilization of TRUs in VHTRs is explored to stabilize in-core fuel compositions (core self-stabilization) leading to extended single-batch OTTO (Once-Through-Then-Out) modes of operation without intermediate refueling.

Open multiple effect desalination with low temperature process heat

Design and in demonstration units proven conception of a desalination system are presented: an ambient pressure, free convection operated counter-current process of evaporation and condensation achieves in a two-stage version a gained-output-ratio of about 6, i.e., about 115 kWh thermal process heat of 85 °C are sufficient for the production of 1 m 3 fresh water. The construction is simple and maintenance easy. The fresh water production cost is estimated to be 2 US$/m 3 which includes only investment capital interest of the present demonstration unit. Auxiliary energy is limited to pumping of the saline water through the (plastic) heat exchanger tubing to the top of the about 250 cm high desalination tower.