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.     

Operation of a semi-technical pilot plant for nuclear aided steam gasification of coal

After intensive investigations on a small scale, the principle of the process has been tested in a semi-technical pilot plant. In its gasifier a fluidized bed of approx. 1 m² cross-section and of up to 4 m height is operated at 40 bar. Heat is supplied to the bed from an immersed heat exchanger with helium flowing through it, which is heated electrically. The plant was commissioned in 1976 and has been in hot operation for approx. 23 000 h, over 13 000 h whereof account for coal gasification. Roughly 1 600 t of coal have been put through. During recent years the processing of German caking long-flame gas coal and the marked improvement of the process by the use of catalysts have been demonstrated successfully.     

Design and experiment of hot gas duct for the HTR-10

A horizontal coaxial double-tube hot gas duct is a key component connecting the reactor pressure vessel and the steam generator pressure vessel for the 10 MW High Temperature Gas-cooled Reactor—Test Module. Hot helium gas from the core outlet flows into the steam generator through the liner tube, while helium gas after being cooled returns to the core through a passage formed between the inner tube and the duct pressure vessel. Thermal insulation material is packed into the space between the liner tube and the inner tube to resist heat transfer from the hot helium to the cold helium. The thermal compensation structure is designed in order to avoid large thermal stress because of different thermal expansions of the duct parts under various conditions. According to the design principal of the hot gas duct, the detailed structure design and strength evaluation for it has been done. A full-scale duct test section was then made according to the design parameters, and its thermal performance experiment was carried out in a helium test loop. With helium gas at pressure of about 3.0 MPa and a temperature over 900 °C, the continuous operation time for the duct test section lasted 98 h. At a helium gas temperature over 700 °C, the cumulative operation time for the duct test section reached 350 h. The duct test section also experienced 20 pressure cycles in the pressure range of 0.1–3.4 MPa, 18 temperature cycles in the temperature range of 100–950 °C. Thermal test results show an effective thermal conductivity of the hot gas duct thermal insulation is 0.47 W m⁻¹ °C⁻¹ under normal operation condition. In addition, a hot gas duct depressurization test was carried out; the test result showed that the pressure variation occurred on the liner tube was not more than 0.2 MPa for an assumed maximum gas release rate.     

Vapour void fraction in subcooled flow boiling

Experimental data on steam void fraction and axial temperature distribution in an annular boiling channel for low mass-flux forced and natural circulation flow of water with inlet subcooling have been obtained. The ranges of variables covered are: mass flux = 1.4 × 10⁴−1.0 × 10⁵ kg/hr m²; heat flux = 4.5 × 10³−7.5 × 10⁴ kcal/hr m²; and inlet subcooling = 10–70°C. The present and literature data match well with the theoretical void predictions using a four-step method similar to that suggested by Zuber and co-workers.     

Effect of Heating and Power Plants on the Environment

The OAO Gazprom has proposed that the consumption of natural gas by heating and power plants in Russia be decreased by 30 billion m³ per year and that this volume of gas be replaced by coal. Data on the environmental effects and effects on human health resulting from enterprises in the coal industry and heating and power plants burning coal and natural gas are analyzed. The volume of emissions of harmful substances into the atmosphere when 30 billion m³ of gas are replaced at heating and power plants by kansko-achinsk and hard kuznets coal is calculated (for three variants). The calculations show that decreasing the amount of gas burned by heating and power plants and increasing at the same time the consumption of coal results in a substantial increase in harmful emissions into the environment.     

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.     

On the heat transfer crisis in steam-generating pipes

The present article provides the results obtained in investigating the heat transfer crisis in the boiling of water in a vertical pipe for the case of forced motion of the steam-water mixture. The investigations were performed at a pressure of 150 atm abs in the range of mass velocities from 850 to 7000 kg/m²sec and of thermal loads of (0.46–1.65) × 10⁶ kcal/m²hr. The mechanism of the development of the heat transfer crisis for an annular flow is described. Empirical formulas for the determination of critical thermal loads are recommended.     

Thermal effects and component cooling in Magnum-PSI

Magnum-PSI is a linear plasma generator, built at the FOM-Institute for Plasma Physics Rijnhuizen. Subject of study will be the interaction of plasma with a diversity of surface materials. The machine is designed to provide an environment with a steady state high-flux plasma (up to 10²⁴ H⁺ ions/m² s) in a 3 T magnetic field with an exposed surface of 80 cm² up to 10 MW/m². Magnum-PSI will provide new insights in the complex physics and chemistry that will occur in the divertor region of the future experimental fusion reactor ITER and reactors beyond ITER. The conditions at the surface of the sample can be varied over a wide range, such as plasma temperature, beam diameter, particle flux, inclination angle of the target, background pressure and magnetic field. An important subject of attention in the design of the machine was thermal effects originating in the excess heat and gas flow from the plasma source and radiation from the target.     

Characteristics of heat transfer of models of core and steam generator surfaces with regulation of impurity content in a loop with lead coolant

The results of experimental investigations of the heat transfer by lead coolant in the ring-shaped gaps of a circulation loop during monitored and controlled mass transfer and mass exchange of oxygen and impurity are presented. The investigations were performed in a loop with circulation of lead coolant at temperature of 450–550°C, average velocity 0.1–1.5 m/sec, Peclet number 500–6000, and heat flux 50–160 kW/m². The oxygen content in the loop was varied from the value for thermodynamic activity 10⁻⁵–10⁰ to saturation and above with formation of lead oxide deposits on the heat transfer surface. The processes in a non-isothermal liquid metal loop with heating (core) and cooling (steam generator) experimental sections simulate the dependence of the heat transfer characteristics in the loop on the impurity mass transfer. __________ Translated from Atomnaya énergiya, Vol. 104, No. 2, pp. 74–80, February, 2008.     

Effective thermal conductivity of MOX raw powder

The radial temperature distribution of plutonium and uranium mixed oxide powder loaded into a cylindrical vessel was measured in air and argon gas, and the effective thermal conductivity was calculated from the measured temperature distribution and the decay heat. The effective thermal conductivities were small values of 0.061-0.13 W m^-1 K^-1 at about 318 K, and changed significantly with O/M, bulk density and atmospheric gas. The results in this work were analyzed by the model of Hamilton and Crosser and a new model for the effective thermal conductivity of the powder was derived as functions of powder properties and thermal conductivity of atmospheric gas.     

The application of nuclear process heat for hydrogasification of coal

Hydrogasification is the conversion of coal with hydrogen to methane. Because coal and water only are primarily available for gasification purposes, the hydrogen required for methane production has to be produced by the gasification process. This requires heat at a high temperature level which can be supplied by a high temperature reactor as nuclear process heat. In this paper two process variants are described for hydrogasification of lignite with nuclear process heat. The design data of a draft for commercial-scale plants are given. Also, the pilot plant of Rheinische Braunkohlenwerke AG for hydrogasification of coal in the fluidized bed is described.     

High heat load properties of actively cooled W/CuCrZr mock-ups by diffusion bonding with Ni or Ti interlayer

Two actively cooled mock-ups with 5 mm thick tungsten armor, joined to CuCrZr alloy, were successfully developed by diffusion bonding technique with Ti or Ni interlayer for the EAST device in ASIPP. Its thermal response and thermal fatigue properties were investigated with active cooling. No cracks and voids occurred at the interface of W/CuCrZr after thermal response test with a heat flux from 0 MW/m² to 10 MW/m². It survived up to 200 cycles under 10 MW/m². The temperature distributions of the mock-up were estimated by Finite Element Analysis. The simulation results indicated that thermal contact capability between the tungsten and the copper alloy with Ti interlayer was higher than that of Ni interlayer. Results showed that diffusion bonding of W/CuCrZr with Ni or Ti interlayer is a potential candidate for a high heat resistance armor material on plasma facing components (PFC).     

Heat flux capabilities of first-wall tube arrays for an experimental fusion reactor

A preliminary design study has been made of some of the thermomechanical problems of water and helium cooling for the first wall of a near-term experimental fusion reactor. The first wall is envisioned as an array of 316 stainless steel tubes between the plasma and the blanket modules to intercept a heat flux from the plasma estimated to be between 0.25 and 1.0 MW/m². Evaluations have been made of the maximum allowable heat fluxes for constraints imposed on the tube wall temperature, the cyclic stresses, the quasi-steady stresses and energy recovery from the coolant. For tubes with 2 meter long heated sections, 10 mm inside diameter and 1 mm wall thickness, water cooling was found to be more than adequate for plasma heat fluxes over 1 MW/m² with a fatigue life of 10⁶ cycles; for a 2 mm wall thickness, at least 0.7 MW/m² can be handled for the same fatigue life. Helium-cooled tubes can also handle heat fluxes up to about 1 MW/m² with a 1 mm tube wall thickness and over 0.5 MW/m² with a 2 mm tube wall thickness, but the required pumping powers tend to be high. The problems of plasma disruptions and erosion by energetic plasma ions are also discussed briefly.     

Methane from synthesis gas and operation of high-temperature methanation

The methanation process is an important unit in generating substitute natural gas (SNG) from coal and in providing heat in the Long-Distance Nuclear Energy Transport (NFE) system. Procedures for methanizing synthesis gases containing CO, CO₂ and H₂ have been developed and tested at the Kernforschungsanlage Jülich GmbH (KFA - Federal Republic of Germany) since 1976. This is being carried out together with the partner in the NFE Project, Rheinische Braunkohlenwerke AG, Cologne (FRG).It has been demonstrated in several thousand operating hours at the KFA since 1979 that the procedures and components developed, as well as the catalysts employed satisfy the demands made by high-temperature methanation in the three-stage methanation plants ADAM I and ADAM II with a SNG gas production of 200 or 3300 m³ (STP)h⁻¹ and a useful heat capacity of 300 kJ/s or 5.8 MJ/s.In 1981 a single-stage pilot plant was put into operation at the KFA in which one reactor with cooled stepped reaction tubes and catalytic fixed beds was utilized. The test operation of 1100 hours shows that at a high gas load on the reaction tubes, thermodynamic equilibrium with a high methane content in the product gas can be achieved with simultaneous steam production at 100 bar.     

Evaluation of heat transfer by sublimation for the application to the divertor heat sink for high fusion energy conversion

Thermal and structural responses of divertor target were evaluated by using finite element method. High heat flux simulating ELMs at the level of 100 MW/m² was assumed onto the tungsten armor, and surface temperature profile was obtained. When dynamic heat load over 100 MW/m² was applied, the maximum surface temperature exceeded 1300 °C, and it caused recrystallization of tungsten regardless of the heat transfer below it. The result was used to conduct dynamic heat load experiment on tungsten, and material behavior of tungsten was evaluated under dynamic heat load. This study also proposed new concept of divertor heat sink which can distribute high heat flux and transfers the heat to high temperature medium. It consists of tungsten armor, composite enhanced with high thermal conductivity fiber, and heat transport system applying phase transition. High heat flux simulating ELMs was also applied to target surface of the divertor, temperature gradient, thermal stress of tungsten and composite were evaluated. Based on the results of analysis, thermal structural requirement was considered.     

Ablation of Fusion Materials Exposed to High Heat Flux in an Electrothermal Plasma Discharge as a Simulation for Hard Disruption

Electrothermal plasma sources operating in the confined controlled arc discharge regime produce heat fluxes in the range expected for hard disruptions in future large tokamaks. The radiative heat flux produced inside of the capillary discharge channel is from the formed high density (10²³–10²⁷/m³) plasma with heat fluxes of up to 125 GW/m² over a period of 100 μs, making such sources excellent simulators for ablation studies of plasma-facing materials in tokamaks during hard disruptions. Graphite, beryllium, lithium, stainless steel, tungsten, copper, and molybdenum are among the materials proposed for use in fusion reactors. Computational experiments with the ETFLOW code using heat fluxes between 10 and 125 GW/m² have shown low total erosion for the low-z materials Li, Be and C and higher erosion for high-z materials Fe, Cu, Mo and W. The time rate of material erosion for various ranges of heat fluxes shows increased erosion with time evolution over the 150 μs pulse length of the simulated disruption event. At the highest values of simulated heat flux, low-z materials were found to ablate almost identically. At all simulated values of heat flux, the ablation of high-z materials correlated positively with the z-number.     

Thermo-mechanical calculations on operation temperature limits of tungsten as plasma facing material

Tungsten is a candidate material as a plasma facing material in the next step fusion devices. The material surface will be exposed to transient heat loads as well as steady-state heat loads. The present work describes the thermo-mechanical analysis of tungsten by finite element calculation. It is shown that tungsten has a strict operational temperature limit under transient heat loads. For the ITER-grade W, the operation limit of the base surface-temperature was calculated to be in a range of 400-780 °C under an applied transient heat load of 0.2 GW/m² for 0.5 ms in order to avoid plastic deformation of W.     

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.     

Radiation damage effects in candidate titanates for Pu disposition: Zirconolite

Results from studies of radiation-induced damage from the alpha decay of ²³⁸Pu on the density and crystal structure of a nominally phase-pure zirconolite and two other zirconolite-bearing ceramics are discussed. Macro and micro swelling were found to be temperature independent, whereas the density determined with He gas pycnometry was temperature dependent. Approximately 2.6 × 10¹⁸ α/g were needed to render the specimens X-ray amorphous- more to saturate the swelling. Unlike pyrochlore-based ceramics, we did not observe any phase changes associated with storage temperature and damage ingrowth. The forward dissolution rate at a pH value of 2 for material containing essentially all zirconolite is 1.7(4) × 10⁻³ g/(m² d) with very little pH dependence and no dependence on the amount of radiation-induced damage. Even after the radiation-induced swelling saturated, the specimens remained physically intact with no evidence for microcracking. Thus, the material remains physically a viable material for the disposition of surplus weapons-grade Pu.