Evaporation forward feed

Liquor containing 5 per cent solids is fed at 340 K to a four-effect evaporator. Forward feed is used to give a product containing 28.5 per cent solids. Do the following figures indicate normal operation If not, why not ... 

Figure 17. Patterns ofliquid flow in multiple-effect evaporators Forward feed, Backward feed, fcj Mixed Feed.

From assumed feed temperature (forward feed) or feed flow (backward feed) to the first effect and assumed steam flow, calculate evaporation in the first effect. Repeat for each succeeding effect, checking intermediate assumptions as the calculation proceeds. Heat input from condensate flash can be incorporated easily since the condensate flow from the preceding effects will have already been determined. 

A forward-feed double-effect evaporator, having 10 m2 of heating surface in each effect, is used to concentrate 0.4 kg/s of caustic soda solution from 10 to 50 per cent by mass. During a particular run, when the feed is at 328 K, the pressures in the two calandrias are 375 and 180 kN/m2 respectively, and the condenser operates at 15 kN/m2. For these conditions, calculate ... 

A forward-feed double-effect standard vertical evaporator with equal heating areas in each effect is fed with 5 kg/s of a liquor of specific heat capacity of 4.18 kJ/kgK, and with no boiling-point rise, so that 50 per cent of the feed liquor is evaporated. The overall heat transfer coefficient in the second effect is 75 per cent of that in the first effect. Steam is fed at 395 K and the boiling-point in the second effect is 373 K. The feed is heated to its boiling point by an external heater in the first effect. 

A double-effect forward-feed evaporator is required to give a product which contains 50 per cent by mass of solids. Each effect has 10 m2 of heating surface and the heat transfer coefficients are 2.8 and 1.7 kW/m2 K in the first and second effects respectively. Dry and saturated steam is available at 375 kN/m2 and the condenser operates at 13.5 kN/m2. The concentrated solution exhibits a boiling-point rise of 3 deg K. What is the maximum permissible feed rate if the feed contains 10 per cent solids and is at 310 K The latent heat is 2330 kJ/kg and the specific heat capacity is 4.18 kJ/kg under all the above conditions. 

A salt solution at 293 K is fed at the rate of 6.3 kg/s to a forward-feed triple-effect evaporator and is concentrated from 2 per cent to 10 per cent of solids. Saturated steam at 170 kN/m2 is introduced into the calandria of the first effect and a pressure of 34 kN/m2 is maintained in the last effect. If the heat transfer coefficients in the three effects are 1.7, 1.4 and 1.1 kW/m2K respectively and the specific heat capacity of the liquid is approximately 4 kJ/kgK, what area is required if each effect is identical Condensate may be assumed to leave at the vapour temperature at each stage, and the effects of boiling point rise may be neglected. The latent heat of vaporisation may be taken as constant throughout. 

Multiple-effect evaporator with forward feed. 

As a second example, consider the classic multiple effect evaporator with forward feed, illustrated in Fig. 20. The problem is as follows ... 

Figure 14.5. Forward-feed arrangement for a triple-effect evaporator...

Figure 14.8. Effect of feed temperature on the operation of a triple effect evaporator (a) Forward feed...

A double-effect forward-feed evaporator is required to give a product which contains 50.0 per cent by mass of solids. Each effect has 10 m2 of heating surface and the heat transfer coefficients are 2.8 and... 

It will also be possible by relatively minor piping changes to convert the forward-feed evaporator to backward feed, which might be more favorable if the calcium sulfate scale problem can be solved. Except for tubes, pump shaft sleeves, impellers, etc., the plant will be built exclusively of steel and cast iron. Tube materials will be evaluated by tubing different evaporator effects and heat exchangers with steel, admiralty metal, aluminum brass, and 90/10 cupronickel. The copper alloy tubes will be used exclusively in the final condenser and in the few heat exchangers that are in contact with nondeaerated sea water. 

Ethvlene reactor, 573.574.588.593 circulating sand, 593 flame reactor, 573 Evaporators, 208-211 backward and forward feed, 211 heat transfer coefficients, 211 sketches, 209-211 thermal economy, 210 Extended surfaces, heat transfer, 188... 

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