Study On Warming Technology Of Multiphase Flow Pool

In alpine pastoral area, temperature is the key factor to influence the gas production rate of biogas digester. In order to guarantee the biogas fermentation operate normally, the digester should take appropriate heat preservation measures and equip a set of corresponding warming system. However, the currently used static warming methods are non-uniform heating and low thermal efficiency, while the dynamic warming methods are complex and hard to be cleaned. In terms of current problems, this paper designed the a new model of multiphase flow pool heating system with the fluidization technology which took the biogas slurry as fluidizing medium, and analysis the performance of this system by numerical simulation.Based on the techno-economic thickness calculation of insulation layer, this paper established the heat transfer calculation model of multiphase flow pool heating system, calculated the heat loss of this system with research site (Kangding county of Ganzi region in Sichuan province) climate conditions, and compared the system efficiency of middle-temperature fermentation(35℃) and high-temperature fermentation(55℃). The results showed that the heat loss mainly comes from the heat loss of materials when it in and out of the digester. This part of the heat loss was closely related and fermentation temperature, environment temperature, and is closely related to the fermentation temperature, environment temperature and fermentation period. The heat loss of digester body and water tank were affected by environment temperature and fermentation temperature, but didn’t affected by fermentation period. This system has a better efficiency under the middle-temperature fermentation(35℃).Because of the complexity of the multiphase flow pool, this paper have done a lot of simplification on modeling and setup of solver through the analysis of literatures combine with the characteristics of the multiphase flow pool. After verified the grid independence of model, we used FLUENT to compared characters of temperature fields under two kinds of boundary conditions——heat dissipation boundary with insulating layer and adiabatic boundary. And then we simulated the flow field and temperature field with five water inlet velocities (0.001 Om/s、0.0015m/s、0.0020m/s、0.0025m/s、0.0030m/s).Then we analyzed the characteristics of flow field, solid-phase distribution and temperature field in the condition of same inlet velocity and different inlet velocities. In order to quantifying solid-phase distribution uniformity, the paper puts forward taking the gini as its index during analysis process.The simulation results showed that the distribution feature and the fluctuation tendency of the temperature under two thermal boundary conditions are similar, but the temperature in outlet pipe was decreased by 1K. Therefore, in order to heat the fermentation liquid to the 35 ℃, it can turn up the entering water temperature around 1K in real operation.It also showed that the increase of solid-phase volume fraction can enhance the disturbance of flow field and is beneficial to the distribution uniformity of solid-phase. However, due to the existence of vortex and backmixing in the internal flow filed, solid-phase distribution was changing all the time. It makes the solid-phase volume fraction was not single positive correlation of distribution uniformity. The internal temperature rise faster than the rate of solid-phase expansion in biogas digester. In the main distribution area of solid state material, the temperature was almost tends to uniformity and achieved uniform warming result in biogas digester. In terms of the whole region, the warming effect is enhanced when water inlet velocity was increased, but for the main distribution area of solid-phase, the warming effect are basically the same under different water inlet velocities. Along with this increase of inlet velocity, solid-phase distribution uniformity decreased slightly while the temperature of outflow water increased slightly, but the hot water loss time had been greatly reduced. Higher inlet flow velocity could reach a better economy. The velocity should be chosen according to actual needs.