Nuclear process heat—application to coal gasification

The high temperature gas cooled reactor has achieved peak coolant temperatures from 775 to 950°C, depending on the core design. These temperatures are sufficiently high to consider the HTR as a source of heat for several large industrial processes. In this article the application is to a coal gasification process which produces a mixture of carbon monoxide and hydrogen as the key product. The gasifier system itself is coupled to the HTR via a catalyzed fluidized bed coal gasifier operating at 700°C and producing methane. The feed to this gasifier is a mixture of carbon monoxide, hydrogen and steam with the stoichiometry chosen to effect an overall athermal reaction so that no heat is directly transferred into the gasifier. Its hydrogen supply is generated by steam reforming the methane produced using the direct HTR heat. This indirect system has advantages in terms of its final product, indirect heat transfer and ultimately in the savings of approximately 40% of the coal which would otherwise have been assumed in an all-coal process producing the same final product.     

Results from the operation of a semi-technical test plant for brown coal hydrogasification

The Rheinische Braunkohlenwerke AG has built and has been operating a semi-technical pilot plant for hydrogasification of coal in fluidized bed. The objective is to develop a coal gasification process with hydrogen for producing directly substitute natural gas. Between 1976 and 1982, the semi-technical pilot plant was operated for about 27000 h under test conditions, more than 12000 h of which were under gasification conditions. During this time, approximately 1800 metric tons of dry coal were gasified. The longest coherent operational phase under gasification conditions was 748 h in which 86.4 metric tons of dry lignite were gasified. Carbon gasification rates up to 82% and methane contents in the dry raw gas (free of N₂) up to 48 vol% were obtained. A detailed evaluation of the test results provided extensive information on the influence of operational parameters on the efficiency dates of the gasifier. Moreover, several components were tested for which no operational experience had previously been gained; these were newly developed devices, e.g. the inclined tube for feeding coal into the fluidized bed. Within the framework of scale-up to large-scale coal gasification plants, a pilot plant having a capacity of about 10 metric tons of dry brown coal per hour was commissioned in late 1982. On May 30, 1983, coal was for the first time fed into the plant. The present test planning provides for tests with brown coal till the end of 1985. This could be followed by the use of other coals, such as hard coal.     

Coal gasification with heat from high temperature reactors: Objectives and status of the project “Prototype Plant for Nuclear Process Heat (PNP)”

It is by now fairly widely known that the high temperature reactor (HTR) is a unique nuclear energy source which can supply heat at temperatures up to 1000°C for application in chemical processes, for which previously exclusively combustion heat sources have been used. With the HTR, it is possible to apply nuclear energy not only for electrical power production but also for the synthesis of liquid or gaseous energy carriers. Nuclear coal gasification appears most promising as the first step for the demonstration and industrial application of nuclear process heat technology in the Federal Republic of Germany. Reactor manufacturers and coal mining companies in co-operation with the Nuclear Research Center at Jülich established a joint project in 1975 for the development of an HTR with a coolant outlet temperature of 950°C, for the development and testing of nuclear coal gasification, for the detailed engineering of a prototype plant consisting of an HTR and gasification plant and finally for the construction and operation of this prototype plant for nuclear process heat (PNP). This contribution describes the status of the PNP-Project and the scope for future development.     

The high temperature gas-cooled reactor as a source of high temperature process heat

The nuclear reactor has established itself as a future major supplier of electrical energy. The industrial market for other forms of energy, however, is almost as large and represents a new potential for the use of nuclear reactors. The high temperature gas-cooled reactor (HTGR) has been developed for commercial application in the electric power generation field. Since the HTGR is capable of delivering process heat in the temperature range of 1000–1500°F, it has many applications that would not be possible at the lower operating temperatures of water-cooled reactors. This paper briefly summarizes the development of the HTGR and outlines its salient technical features. Modifications to the reactor that enable it to be used as a process heat source are discussed. Specific applications are developed for coal gasification, steelmaking, and hydrogen production.     

Materials for coal gasification plants utilizing nuclear process heat generated in a high temperature reactor

In coal gasification plants based on nuclear process heat, materials are subjected to high temperature corrosion in process gas atmosphere at 750 to 900° C. The process gas consists of steam, CO, CH₄, CO₂ and, depending on the gasified coal, low or high H₂S-concentrations. Materials for heat exchangers must be resistant to high temperature corrosion. They should also have adequate creep rupture strength. Therefore the commercial alloy Incoloy 800 and various model alloys were exposed to a process gas atmosphere to determine the corrosion behaviour and also stressed mechanically to investigate the interaction of high temperature creep behaviour and corrosion.

Compared with Incoloy 800, one of the new model alloys (30–32% Ni, 25–27% Cr, and Ce, Fe-balance) exhibits a very good corrosion resistance even when sulphur rich coal is gasified. The creep rupture strength at 900° C is in the range of the creep strength for Incoloy 800.     

Nuclear powered heat pumps for near-term process heat applications

There is a substantial market for nuclear energy in non-electric applications such as hydrogen production or water desalination. Among the Generation IV reactor concepts, the very high temperature reactor (VHTR) with a reactor outlet temperature close to 1000 °C and a power conversion efficiency of approximately 50% is believed to be the most suitable concept for co-generation of process heat. Its high coolant exergy would enable centralized hydrogen production and other process heat applications. In this paper it is shown that a reactor with lower coolant outlet temperature or another near-term heat source can also meet the VHTR objectives which are high power conversion efficiency and capability to deliver high temperature process heat in the narrow temperature window required by thermochemical hydrogen production cycles. The approach was to separate the requirement for high temperature process heat production from the nuclear part of the plant, in other words the nuclear part of the power plant would run at acceptably low temperature while the high temperature heat production via a heat pump system would be limited to a conventional external circuit, thus avoiding nuclear constraints. The separation of these high temperature constraints from the reactor would avoid massive R&D requirements on materials, components and fuel with uncertain outcome thus unnecessarily delaying introduction of this otherwise very attractive reactor concept.We then show that the proposed technology is equally suitable for the generation of cold (e.g. for air conditioning) and for desalination of seawater.     

The HTR for process heat application according to the BBC/HRB-concept

The development of the High-Temperature Reactor (HTR) for the generation of nuclear process heat for coal gasification applying temperatures up to 950°C is one of the most important long-term HTR-development objectives pursued within the German PNP-project. The HTR for nuclear process heat generation according to the concept of BBC/HRB is part of the commercialization strategy of the HTR-line, which is based on the preceding AVR experimental reactor, the THTR-300 MW_c prototype plant and the HTR-500 MW_c plant. This strategy permits an optimum utilization of the development of the nuclear heat supply system of the THTR-300 and HTR-500 and represents a consequent continuation of the German HTR development pursued up to now. It will result in the lowest possible cost and time expenditure on the commercialization of the HTR for all applications. A new reactor development is not required with this concept. The earliest possible realization of a first-of-its-kind nuclear process heat plant will be determined by the development of the gasification processes.     

Experiments for combining nuclear heat with the methane steam-reforming process

A high temperature reactor with the cooling gas helium leaving at an average temperature of 950°C offers an interesting possibility for combining nuclear heat with the methane steam-reforming process. However, the incorporation of nuclear heat into this process still requires comprehensive experimental and theoretical studies before an economic and technical optimization of a combined nuclear/chemical plant can be reached. Thus the EVA (single reforming tube, Einzelrohr-Versuchsanlage) pilot plant was set up to examine the methane steam-reforming process in a helium-heated conventional reforming tube. This report describes the plant and specifies some representative experimental results. It follows that convective helium heating is an appropriate method of transferring heat to the reforming tube. In addition, the report describes two accompanying experiments in smaller high pressure test plants and summarizes some of the measured results.     

Layout of an internally heated gas generator for the steam gasification of coal

Industrial-scale steam gasification of coal using heat from high temperature reactors requires research and development on allothermal gas generators. Bergbau-Forschung GmbH, Essen, does theoretical and experimental work in this field. The experiments deal with reaction kinetics, heat transfer and material tests. Their significance for the layout of a full-scale gas generator is shown. Including material specifications, the feasibility of a gasifier, characterized by a fluid bed volume of 318 m³ and a heat transferring area of 4000 m², results. The data, now available, are used to determine the gasification throughput from the heat balance, i.e. the equality of heat consumed and heat transferred. Throughputs of about 50 t/hr of coal are possible for a single gas generator, the helium outlet temperature of the HTR being 950°C. Bergbau-Forschung has commissioned a medium-scale pilot plant (200 kg/hr).     

Synergistic hydrogen production by nuclear-heated steam reforming of fossil fuels

Processes and technologies to produce hydrogen synergistically by the nuclear-heated steam reforming reaction of fossil fuels are reviewed. Formulas of chemical reactions, required heats for reactions, saving of fuel consumption, reduction of carbon dioxide emission, and possible processes are investigated for such fossil fuels as natural gas, petroleum and coal.

In this investigation, examined are the steam reforming processes using the “membrane reformer” and adopting the recirculation of reaction products in a closed loop configuration. The recirculation-type membrane reformer process is considered to be the most advantageous among various synergistic hydrogen production processes. Typical merits of this process are; nuclear heat supply at medium temperature around 550°C, compact plant size and membrane area for hydrogen production, efficient conversion of a feed fossil fuel, appreciable reduction of carbon dioxide emission, high purity hydrogen without any additional process, and ease of separating carbon dioxide for future sequestration requirements.

The synergistic hydrogen production using fossil fuels and nuclear energy can be an effective solution in this century for the world which has to use fossil fuels to some extent, according to various estimates of global energy supply, while reducing carbon dioxide emission.     

核能制氢技术的发展

氢是清洁能源,有非常好的应用前景.但氢是二次能源,需要利用一次能源来生产.以可持续的方式(原料来源丰富、无温室气体排放)实现氢的大规模生产是实现氢广泛利用的前提.核能是清洁的一次能源,核电已经成为世界电力生产的主要方式之一.正在研发的第四代核能系统除了要使核电生产更经济和更安全之外,还要为实现核能在发电之外的领域的应用...     

Gasification of coal with steam using heat from HTRs

In existing coal gasification processes a substantial part of the coal is used to provide the heat for the reaction, for the generation and superheating of steam and for the production of oxygen. By using heat from HTRs to substitute this part, the coal is then completely used as raw material for gas production. This offers the following advantages compared with the existing processes: a saving of coal, less CO₂ emission and, in countries with high coal costs, lower gas production costs. A survey is given of the state of the project, discussing the first design of a commercial gasifier, the influence of the helium outlet temperature of the HTR, kinds of products, and the overall efficiency of the plant. The aim of the development is to demonstrate the use of heat from an HTR for full scale coal gasification, starting in 1985.     

Study on efficiency of DCP for nuclear hydrogen production

With many advantages, hydrogen is considered as the fuel of the future. But there is no natural resource of hydrogen and it must be produced by other kinds of energy. As for the primary energy, nuclear energy is a promising alternative. Using heat from nuclear reactor to produce hydrogen is receiving more and more concerns in recent years. This paper mainly emphasizes the study of the direct contact pyrolysis （DCP） of methane using heat from nuclear reactor. A facility was designed to investigate the efficiency of DCP process in certain conditions. The experimental results show that this process produces only hydrogen and carbon. The conversion efficiency increases with temperature and residence time, but decreases as flow rate increases. The highest efficiency of DCP obtained in this exoedment is about 22%.     

Studies on the permeation of hydrogen and tritium in nuclear process heat installations

To realistically evaluate the important problems of hydrogen and tritium permeation in nuclear heated high temperature systems, estimates are made, among others, on the basis of the authors preliminary experimental data. Steam-methane reforming is used as the key process. The results show that oxide layers can decrease the hydrogen permeation rate by more than two orders of magnitude and that not only the oxidation potential and temperature but also the water partial pressure may be essential for the formation and possibly the structure of oxide layers, and consequently for the permeation rate. The consequences of the experimental data for the permeation of tritium are also discussed. The available empirical data and results of the measurements discussed here still contain large uncertainties. It will therefore be necessary to carry out, under as realistic conditions as possible, a broad parameter study of heat exchanger materials which are seriously considered for use in nuclear process heat installations.     

South Africa's opportunity to maximise the role of nuclear power in a global hydrogen economy

Global concern for increased energy demand, increased cost of natural gas and petroleum, energy security and environmental degradation are leading to heightened interest in using nuclear energy and hydrogen to leverage existing hydrocarbon reserves. The wasteful use of hydrocarbons can be minimised by using nuclear as a source of energy and water as a source of hydrogen. Virtually all hydrogen today is produced from fossil fuels, which give rise to CO₂ emissions. Hydrogen can be cleanly produced from water (without CO₂ pollution) by using nuclear energy to generate the required electricity and/or process heat to split the water molecule. Once the clean hydrogen has been produced, it can be used as feedstock to fuel cell technologies, or in the nearer term as feedstock to a coal-to-liquids process to produce cleaner synthetic liquid fuels. Clean liquid fuels from coal - using hydrogen generated from nuclear energy - is an intermediate step for using hydrogen to reduce pollution in the transport sector; simultaneously addressing energy security concerns. Several promising water-splitting technologies have been identified. Thermo-chemical water-splitting and high-temperature steam electrolysis technologies require process temperatures in the range of 850 °C and higher for the efficient production of hydrogen. The pebble bed modular reactor (PBMR), under development in South Africa, is ideally suited to generate both high-temperature process heat and electricity for the production of hydrogen. This paper will discuss South Africa's opportunity to maximise the use of its nuclear technology and national resources in a global hydrogen economy.     

Transport of nuclear heat by means of chemical energy (nuclear long-distance energy)

Nuclear long-distance energy, i.e. the transportation of chemically bound energy, represents a potential application for process heat plants in which the endothermic reaction takes place at the heat source (high temperature reactor) whereas the exothermic back reaction occurs at the region of heat utilization (consumer). Due to the following criteria, i.e. reversibility of the chemical reaction, sufficiently large reaction enthalpy, favourable temperature region for the forward and back reactions, and the available technology, a combination of the methods of endothermic steam reforming of methane and exothermic methanation is chosen. As well as supplying household and industrial consumers with heating, process steam and electrical energy, an interconnected system with synthesis gas consumers (e.g. methanol production and iron ore reduction plants) is possible. It is shown that the amount of reactor heat which is convertible into long-distance energy depends considerably on the helium temperatures in the high temperature reactor and lies between 60 and 73% of the reactor power. Conceivable circuit schemes for the nuclear steam-reforming plants and the methanation plants are described. Finally, it is demonstrated, with the help of a simple model for cost estimations, that the nuclear long-distance energy system can make heating for households available in competition with oil heating and that due to the lower specific transport costs, for distances larger than 50 km it is also more economical than the hot water supply from the thermal power coupling of steam turbine plants using light water reactors (LWRs) or high temperature reactors (HTRs).     

Heat Transfer Performance of High Temperature and High Velocity Hydrogen Flow inside Circle Tube

In order to investigate the thermo-hydraulic characteristics of working fluids in the coolant channel of nuclear thermal propulsion reactors, the flow and heat transfer performance of high temperature and high velocity hydrogen in the circle tube was studied by the numerical calculation method. Comparing with the experimental data, it is found that the pressure-based coupled algorithm, SST k-ω turbulence model and hydrogen property model are reasonable and feasible to simulate the flow and heat transfer performance of hydrogen at high temperature and high velocity. The calculated values agree well with the experimental data, and the numerical simulation model is correct. Based on the analysis of flow and temperature field of the base case, the effects of thermal parameters on the flow and heat transfer performance of hydrogen were also studied. The increasing inlet mass flow rate enhances heat transfer performance and the increasing heat flux weakens it. The methods and results can provide some references and guidance for the study of the flow and heat transfer performance of gaseous fluid under high temperature and high heat flux, and thermal design and simulation of nuclear thermal propulsion reactor.     

高温、高流速氢气在圆管内流动换热特性研究

为探究工质在核热推进反应堆冷却剂通道内的热工水力行为,基于数值计算方法,开展了圆管内高温、高流速氢气流动换热特性研究。通过与实验数据对比发现,采用压力基耦合算法、SST k-ω湍流模型以及物性模型进行高温、高流速氢气流动换热特性数值模拟是合理可行的,计算值与实验值符合较好,计算模型选择正确。在分析基础工况流场与温度场的基础上,还研究了热工参数对氢气管内流动换热特性的影响,结果表明,随质量流量的增大换热效果增强,随热流密度的增大换热效果变差。研究方法与结果可为高温、高热流密度环境下气体工质流动换热特性研究、核热推进反应堆的热工设计与仿真模拟提供参考。