Research On The Hydraulic Design Of LNG Submerged Pump And Implementation Of Pump Prototype

As a kind of clean energy, liquefied natural gas(LNG) is rapidly increasing its market share in the world’s energy supply, and becoming one of the fastest developing petrochemical products in recent years. In the LNG industry, LNG submerged pumps are essential for the transportation of LNG. However, a few foreign corporations monopolize the supply of LNG submerged pumps. In order to break this monopoly and produce our own products, the primary work should be studying on how to design the LNG submerged pump. In this dissertation, hydraulic design, manufacturing and performance test of gas vehicle filling pump were studied, aiming to provide theoretical basis and technique supports for the design and production of LNG submerged pump. Main works are as follows: I. Hydraulic design of the main overflow parts in LNG submerged pumpThe main overflow parts of LNG submerged pump are impeller, inducer and guide vane. Hydraulic models of the main overflow parts were designed, considering both pump performance and structural need.Traditional design theories which are based on one-dimension theory were adopted to the hydraulic design of impeller. When establishing the theoretical head of the designed impeller, local energy loss in the outlet part of the pump was taken into consideration to ensure pump’s total head.Before designing the inducer, its design head should be known according to the Required Net Positive Suction Head(NPSHR) of the primary impeller. Considering CFD can simulate the cavitation flow within the pump, numerical simulations were carried out to estimate the NPSHR of the primary impeller. After this, geometrical parameters of the inducer were established according to hydraulic performance and structural needs.Special structural design was introduced to the guide vane, which is good for reducing the pump’s radial size. Since no specific design method for this kind of guide vane could be found, method for the radial diffuser was referred to when designing the LNG pump guide vane. Then numerical simulation was used to study the effect of guide vane’s key geometrical parameters, inlet width and turning angle, on the pump hydraulic performance. It turns out that inlet width shows great influence to pump performance and optimum value exits, while turning angle seems to be much less important by contrast. II. Prediction of LNG submerged pump hydraulic and cryogenic cavitation performanceNumerical simulation of the LNG submerged pump was presented to predict the hydraulic and cryogenic cavitation performance after the hydraulic design. For the hydraulic performance prediction, the computational geometry model included the whole overflow parts of LNG submerged pump, and three-dimensional steady numerical simulations were carried out under different flow rates. For the cavitation performance prediction, the computational geometry model only considered the inducer and primary impeller, and both isothermal and thermal models were used to present the thermal effect of cryogenic liquid on cavitation simulation. It is found that the hydraulic performance of designed LNG submerged pump reaches the requirements. The head curve is smooth at low flow rates, but drops faster at high flow rates. And the designed pump has wide operation range with high efficiency. As to the cavitation performance, thermal effect turns out to be significant. The predicted NPSHR of this cryogenic pump is smaller when using thermal model than that when using isothermal model. III. Prototype manufacturing and performance testOn the basis of the pump design, a pump prototype was manufactured. To validate the hydraulic performance of the prototype pump, liquefied nitrogen tests on both our prototype pump and the imported pump with the same design parameters were carried out. Test results show that our prototype pump functions well and has higher head than the imported pump under different flow rates. As to the pump device efficiency, imported pump performs better than our prototype pump at low flow rates, while just the opposite at high flow rates, which is good for pump’s actual operation.