Evaluation of the efficiency of an unreacted hydrogen removal system based on an experimental model

Based on the Russian Energy Development Strategy to 2050, the nuclear power industry faces the task of increasing flexibility by reducing load to 50% of its nominal capacity. A number of reasons are presented, leading to the conclusion that reducing NPP load is clearly unprofitable and ineffective. Therefore, a rationale is provided for providing NPPs with baseload power using a hydrogen complex through the electrolysis of hydrogen and oxygen, as a promising and competitive energy storage method. Thus, unused NPP capacity during the expected load reduction period is converted into hydrogen and oxygen for subsequent use to generate power during peak periods in the power grid. To achieve this, hydrogen is burned in oxygen in a special combustion chamber, and the resulting high-temperature steam is mixed with steam downstream of the steam generators and upstream of the NPP turbine. The main advantage of using a hydrogen complex is the ability to maintain the NPP’s nominal load (baseload mode) throughout the day. Crucially, the reactor operates at its nominal load. Based on forecast data, a significant increase in the commissioning of electrolysis capacity is noted for the period up to 2050. The authors have a solid scientific foundation in the problem of combining nuclear power plants with hydrogen complexes, having completed assessments of thermodynamic and technical-economic efficiency, as well as competitiveness indicators when compared with the benchmark option – pumped storage power plants. The article focuses on improving safety when using hydrogen to superheat the working fluid of NPP steam turbines due to the presence of unreacted hydrogen and oxygen after the combustion system, which entails the risk of forming an explosive mixture when entering the condenser. The authors previously published an article substantiating the principle of improving safety when using hydrogen in the cycle of NPP steam turbines. This article is a continuation of this work, aiming to theoretically evaluate the reduction in the proportion of unreacted hydrogen in a mixture with oxygen and superheated water vapor using a system for removing unreacted hydrogen based on catalytic recombination and magnetic separation, as well as to evaluate the efficiency of the unreacted hydrogen removal system based on an experimental model. The novelty of the proposed concept lies in its comprehensive principle of improving the safety of using hydrogen when it is burned in oxygen to superheat the working fluid of NPP steam turbines. The article analyzes the global state of the art in the field of catalytic hydrogen recombination, magnetic separation of various gas mixtures, as well as water electrolysis in a magnetic field and membrane hydrogen extraction. Using the example of a VVER nuclear power plant using hydrogen to superheat live steam from a steam turbine plant and the authors’ experience in experimentally studying the underburning of hydrogen during combustion in oxygen, an estimate is given of the possible proportion of unreacted hydrogen in the composition of the working fluid, which amounted to up to 2% by volume, depending on the number of hydrogen-oxygen combustion chambers. The paper presents a schematic diagram of the experimental setup, including a catalytic recombination and magnetic separation unit with a palladium membrane, and a methodology for evaluating the efficiency of the unreacted hydrogen removal system. The operating parameters of the experimental setup are presented. According to the experimental model, a mixture of superheated water vapor, hydrogen, and oxygen is passed through a recombination and magnetic separation unit operating under vacuum, which will lead to a decrease in the proportion of hydrogen in the mixture. The theoretical results of estimating the residual proportion of hydrogen in the mixture and the efficiency of the unreacted hydrogen removal system are presented. As shown by the performed assessments, the proposed system for removing unreacted hydrogen reduces its proportion in the mixture from 2 % vol. to 5,66 ∙ 10-3 % vol. at a pressure of 5 kPa, with the efficiency of the removal system amounting to 99,717%, and to 5,66 ∙ 10-4 % vol. at a pressure of 50 kPa with an efficiency of 99,972%. Thus, the increase in safety is achieved due to the fact that the mixture becomes very lean, since the hydrogen content is reduced by 2-3 orders of magnitude from the lower limit of ignition in a mixture with oxygen, which, with a tenfold reserve according to safety standards, is 0,4% by volume

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