SCWR hydrogen cogeneration model

Supercritical water reactor (SCWR) hydrogen cogeneration is the process of coupling a hydrogen generation plant to a SCWR nuclear reactor to make use of the waste heat of the SCWR to drive the hydrogen generation plant.
Current research in this area has focused on different technologies: the Canada Deuterium Uranium (CANDU) reactor, the United States light water reactor (LWR), and boiling water reactor (BWR) designs. Copper chloride hydrogen co-generation research has focused on the CANDU Super Critical Water Reactor (SCWR) as its integration technology. The basis of CANDU SCWR co-generation system is utilization of high temperature low pressure loop (600°C and 6 MPa) for its hydrolysis and oxygen unit.
Recent Developments
In recent years, starting 2009, significant efforts are underway to develop the hydrogen cogeneration model by CANDU SCWR associated enabling technologies. The CANDU SCWR heat and steam is planned to be used for hydrogen production by copper chloride method which is increasingly viewed as a strong component of zero emission energy technologies. The SCWR is still in its evolution phase; therefore, collaborative efforts are required to better understand SCWR plant materials, chemistry, safety, reliability, and stability methods. It is anticipated that SCWRs would have a combination of advantages of BWRs and PWRs .. The super critical steam generators and turbine design in conventional power plants spans over fifty years . This experience of super critical turbines can be utilized effectively in CANDU SCWR systems. Previous studies focused on conventional SCWR cycle for fossil fuel power plants but by beginning of 2009, there has been a growing interest for the CANDU SCWR cycle . Since CANDU SCWR concept is still in its evolution phase, several optimal configurations such as direct heat cycle, indirect heat cycle and dual reheat steam cycle can be investigated to form an efficient design. Expanding the reactor supercritical steam directly to the high-pressure turbine is more efficient method as temperature is contained within the cycle and replaces the use of expensive steam heat exchangers, dryers and moisture separators but a high-pressure turbine is directly exposed to the reactor steam, which can be a source of radioactive spread in the conventional cycle.
CANDU systems use the indirect method of steam expansion from reactor to the intermediate heat exchangers, dryers and separators. Thermal efficiency is sacrificed in the dual expansion cycle but radiation containment is achieved through dual expansion cycle. The parametric ranges achieved through regenerative loop can be up to 625 °C and 6.3 MPa. These are ideal for the CANDU SCWR hydrogen co-generation model. CANDU SCWR cycle efficiency is improved by employing a regenerative heat mechanism within the SCWR reactor and also into the feed water system. The SCWR heat regeneration is accomplished by recirculation cycle between the HP turbine and the SCWR, which can achieve higher temperature steams at lower pressures. It is suitable for CANDU SCWR hydrogen co-generation model. Steam bleed from high pressure and low pressure turbines is led to feed water system heat exchangers to increase the feed water temperature up to 315 °C. Comparative analyses between no-reheat, single reheat and double reheat reveals that the single reheat CANDU SCWR cycle is optimal considering the design complexity and thermal efficiency of the cycle. The major problem for integrating the hydrogen cycle into the CANDU SCWR cycle is the higher pressures of the SCWR heat transport cycle, which can be controlled by employing bank of dampers in the hydrogen plant low pressure and high temperature intake loop. The higher pressures are necessary to maintain the steam in the supercritical state. The pressure ranges in SCWR with non-regenerative design is 25 MPa and 625 °C while it is from 9 to 6 MPa and 625 °C in the regenerative loop. In copper chloride cycle, the oxygen production, molten copper chloride unit requires 500 °C while hydrochloric cycle requires 430 °C. A lower pressure differential between the integration loops is essential to meet the safety requirements of both the CANDU SCWR and the hydrogen plant.
Copper Chloride Hydrogen Production Unit
Copper Chloride cycle is carbon free and zero-emission technology, that is found more economical and environment friendly than SMR []and electrolytic hydrogen separation method[]. This cycle operates at lesser temperature and is a promising renewable energy source. The copper chloride electrochemical hydrogen production cycle is divided into five major steps.
* Chlorination
* Electrolysis
* Drying
* Hydrolysis
* Decomposition
The heat generated by copper chloride components can meet fifty percent of a plant’s heat requirements. The chlorination, hydrogen production exothermic step occurs at temperatures 450-470°C, producing molten copper chloride and hydrogen gas. The second step of electrolysis is accomplished in an aqueous solution of HCl with temperatures of 30-80°C. The third, endothermic drying step can be accomplished by crystallization with temperature ranges from 30-80°C or by spray drying with temperature ranges from 100-260°C. The fourth endothermic hydrolysis step is accomplished at 375°C. The final step involves endothermic decomposition producing oxygen at 530°C. The chlorination and decomposition steps require higher operating temperatures from 470 to 530°C. Therefore, the CANDU SCWR high temperature and low pressure loop can be interfaced with chlorination and decomposition units. Fig. 1 and 2 show one line diagram for major components of a close loop hydrolysis and oxygen reactor. In hydrogen production, the copper takes many forms such as solid, slurry and molten. In the hydrogen production unit (ion exchange bed) solid copper reacts with high temperature hydrochloric gas to form hydrogen and copper chloride. The hydrogen gas produced has temperatures from 430 to 475°C, which is further cooled down to 25°C by the cooling water and is passed through the purifier before storing it into the hydrogen storage tank. Molten copper chloride produced in an ion exchange bed is spray dried to solid copper chloride and slurried with hydrochloric and water solution. The slurry is then pumped to the conveyor belt for the repetitive cycle. The cooling water exchanging heat with hydrogen gas enters heat exchanger at 25°C and leaves it at 400°C.

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