Mannvit Engineering specializes in anhydrous ammonia storage systems including terminals, atmospheric storage tanks, ship unloading systems, refrigeration systems, transport pipelines and pumping and heating systems to deliver liquid ammonia to the tank. Company specialists offer comprehensive design, engineering and consulting services and have worked on several large-capacity refrigerated ammonia storage tanks and systems.
Large scale distribution of ammonia is usually transported via cargo ships delivered to shipping points in very large volumes. These large volumes need to be contained in a single refrigerated storage tank, usually in the range of 10-60,000 tons - well beyond the practical limit of pressurized storage tanks.
Services include:
Project examples:
1000 ton atmospheric ammonia storage tank in Iceland
Owner: The National Fertilizer Plant, Iceland
The project included a new ammonia terminal, including refrigerated ammonia storage tank, refrigeration system, ship unloading facilities and transport pipeline, pumping and heating system for the liquid ammonia from the tank.
Tank details: The ammonia storage tank is of the refrigerated atmospheric type, with a nominal capacity of 1000 t. The tank has 12 m high sidewall, inner diameter of 13.4 m and outer diameter of 15.3 m. The roof is a sphere shaped dome with a radius of 13.4 m. The foundation is built on elevated concrete walls so that free air can circulate under the tank bottom, thus avoiding a heating system. The tank is a double integrity/double containment type, with a double steel wall design, where the inner tank contains the refrigerated liquid. Additionally there is an earth bund around the tank designed to take all the ammonia in case of rupture. The sidewall and the bottom of the tank are insulated on the outside, but the roof insulation is suspended from the tank roof. The water vapor barrier is especially import to prevent damages to the insulation due to ice build-up.
The design pressure is 180 mbar and the operating pressure is in the range of 40-80 mbar. The design temperature is minus 40C and the operating temperature is in the range of minus 32-33C.
Design standards: mainly BS7777 on refrigerated storage tanks and API620 with Appendix R on refrigerated tanks. For wind, temperature and seismic loadings we used Icelandic standards and regulations. As we have considerable seismic activities in Iceland the tank was calculated for these. We used Icelandic standards and guidelines but also New-Zealand guidelines specially made for seismic design of storage tanks. Additionally we followed other guidelines, especially those related to the critical issues of stress corrosion cracking in ammonia storage tanks.
5000 t atmospheric ammonia storage tank in Sweden
Owner: Akzo Nobel
The project included a complete new ammonia terminal and included new refrigerated ammonia storage tank, refrigerating system, ship unloading facilities, pumping and heating system for the ammonia from the tank. The tank was commissioned in 1997 and is in operation without problems. The project was completed in 19 months.
Tank details: The ammonia storage tank is of the refrigerated atmospheric type, with a nominal capacity of 5000 tons. The tank has 18.5 m high sidewall and a diameter of 24.8 m. The roof is a sphere shaped dome with a radius of 24.8 m. The foundation is built on elevated concrete walls so that free air can circulate under the tank bottom, thus avoiding a heating system. The tank is double integrity, with a single steel wall built into rock, where the rock and concrete wall form the outer tank. The tank is standing in a rock bund of nominal diameter of 30 m. To even out the difference in the level on the top of the rock bund, concrete walls were built. The opening into the rock bund used during construction was closed with a concrete wall when the construction was finished, prior to commissioning of the tank. The sidewall and the bottom of the tank are insulated on the outside, but the roof insulation is suspended from the tank roof. The water vapor barrier is especially import to prevent damages to the insulation due to ice build-up.
The design pressure is 140 mbar and the operating pressure is in the range of 40-70 mbar. The design temperature is minus 40C and the operating temperature is in the range of minus 32-33C.