The coil type single-effect concentrating pan is a continuous feeding and intermittent discharging concentrating equipment widely used in dairy factories. Its structure is shown in the figure. It is mainly composed of coil heater evaporation chamber, foam trap, inlet and outlet valves and It consists of various control instruments.
The pot body is a vertical cylindrical closed structure, the upper space is an evaporation chamber, and the lower space is a heating chamber. The heating chamber is provided with 3-5 sets of heating coils, which are arranged in layers, 1-3 turns per plate. Each set of coils is equipped with a separately operable heating steam inlet and a condensed water outlet, and there are two kinds of inlet and outlet.
The foam trap is centrifugal and is mounted on the outside of the upper part of the concentrator. The foam trap center riser is connected to the vacuum system.
During operation, the liquid enters the pot through the feed tube along the tangential direction of the pot. After the material of the outer coil is heated, the volume expands and floats. When the liquid level is reached, the secondary steam in the liquid escapes, the concentration of the liquid increases, and the density increases. The material in the coil is relatively low in heat and has a high density, which naturally drops back. Thereby, a natural circulation is formed in which the liquid rises along the outer coil and falls back along the center of the coil.
The secondary steam generated by evaporation enters the foam trap from the center of the upper part of the concentrating pot to form a vortex in a tangential direction. Under the action of centrifugal force, the droplets of the liquid entrained in the secondary steam accumulate on the wall of the trap. In the returning pot, the steam from which the milk particles are removed is spiraled up, and is turned to the condenser through the riser.
When the concentration of the material in the concentrating pan reaches the requirement, the heating can be stopped, and the discharge valve at the bottom of the pan is opened.
The coil evaporator has a simple structure, is easy to manufacture, stable in operation, and easy to control. The coil has an oblate circular cross section, and the liquid material has small flow resistance and large passage, and is suitable for liquid materials with high viscosity. Since the heat pipe is short, the temperature of the pipe wall is uniform, the condensed water can be eliminated in time, and the utilization rate of the heat transfer surface is high. The heat transfer area is small, the liquid material convection circulation is poor, and it is easy to scale. It is convenient to independently control the heating steam on and off and the pressure in each coil according to the liquid level of the liquid to meet the production or operation needs. When in use, there must be no steam that is exposed to the liquid surface, and steam can only be supplied after the liquid material is flooded. Due to the large size of the coil structure, the heating steam pressure should not be too high, generally 0.7-1.0 MPa. The feed liquid takes a long time to heat and affects the quality of the product to a certain extent.