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Hydrogen Applications

Central cooling systems for large-scale green hydrogen production can be based on wet or dry cooling . Alternatively , hybrid solutions are available as well . This article discusses three such solutions and considers the factors influencing the selection of cooling technology .

About the company

Kelvion Thermal Solutions ( KTS ) is an expert in heat exchange . KTS normally gets involved in early engineering phases of large projects to help clients in making such technology choices .

By Roy Niekerk , Director Global Sales & Solutions Hydrogen , and Radhouene Manita , Application Engineer , Kelvion Thermal Solutions

The two most established processes for green hydrogen production are alkaline water electrolysis and polymer electrolyte membrane ( PEM ) electrolysis . In both processes , a liquid is recirculated over an electrolyser stack to form hydrogen and oxygen . During the electrolysis process , heat is released , which needs to be cooled away . This cooling step is normally done in a plate and frame heat exchanger . However , more cooling positions in the hydrogen production process are available . Alternating current electricity is changed into direct current , which releases heat . Two further positions are the formed oxygen and hydrogen , which are cooled before further purification . The deeper the cooling , the more water is ‘ knocked out ’ by means of condensation , reducing the required size of the drying section in the plant . Further downstream , the hydrogen is compressed , which requires compression interstage and aftercoolers . A closed loop of water or water-glycol mixture is used to cool all the different coolers in the hydrogen production process . And the closed loop is cooled in a central system . Electrolyser capacity is normally expressed in megawatts . And as a rule of thumb , roughly 25 – 30 % of that capacity is cooled away in the central cooling system . Different cooling methods exist .

Dry or wet cooling Air Fin Coolers ( AFC ) are one method of cooling down a closed loop . Typically , an AFC consists of a series of horizontal finned tube bundles with box headers at each end that run either underneath or above axial fans within a plenum chamber , which directs the air flow . Usually , the air blows upwards through the tube bundles , cooling the hot liquid . But the fans can be configured to forced or induced draft , depending on whether the air is pushed or pulled through the tube bundle . Large-size industrial AFCs offer a great design freedom in terms of plot configurations , header types , and project specifications that need to be followed . A big advantage is that no water is used . As a rule of thumb , the temperature approach in an AFC is 10 ° C . By using special tube technologies such as Groovy-Fin ^® and DIESTA ^® , the temperature approach can in some cases be pushed to 7 ° C , but it is not advisable to use such low values in the initial project development . As an example , if a project designs the system for maximum 30 ° C dry-bulb temperature and Groovy fins are used with 7 ° C approach temperature , the closed loop can be cooled down to 37 ° C as a minimum . Temperature approach in a plate and frame exchanger is 2 ° C . The resulting minimum process temperature is therefore 39 ° C . In regions where water is available , however , open cooling towers can be selected . Water that is sprayed down in the tower is brought in contact with air , which is pulled through the tower fill material by means of a large fan-motor combination . A very small portion of water is evaporated , causing the remaining water to cool down . A big advantage of a cooling tower are the much lower temperatures it can reach compared to dry cooling . In the above-given example , a dry-bulb temperature of 30 ° C was assumed , which is a typical value for Western European locations . In such locations , however , the wet-bulb temperature can be as low as 21 ° C . A rule of thumb for cooling towers is a 4 ° C approach to wet-bulb temperature . In this case ,

Demineralised water

Purification section

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