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The Basic Mass Balance
The simple equation
Changing the variables
Changing the variables
Understanding the simple mass balance of heat transfer is essential and of first order in understanding the evaporation process. It can be expressed by this illustration. Here we have two halves of a square where one half represents the steam side and the other is the product side. These halves could be steam and product plates in a plate & frame evaporator or the shell side and tube side of a tubular evaporator. In its simplest mathematical form, it shows that for every pound of steam that gives up its heat to the colder product as it condenses into a liquid it will conversely boil off pound for pound the same amount of product in the product side.
Therefor If the stem rate remains constant, and the feed flow and it’s % solids remains constant, the end result will be a constant finished product % solids.
Changing the variables
Changing the variables
Changing the variables
In this illustration you can see that the steam input to the mass balance has changed and the results are clear. This is also true if the feed flow changes or if the % solids in the feed changes. If you go to th calculations page you can enter these values and see how changing these variables will effect the final outcome. The point here is that in order for the process to provide a consistent finished product the process variables must be controlled to maintain a steady state.
Other variables not in this basic equation are the affects of fouling which is a resistance to heat flow from the steam side to the product side. It like a layer of insulation forming on the surface of the product side which gets thicker and thicker over time. At some point the product side will need to be cleaned. This is a natural progression of fouling common to most all processes. There is another component know as non condensable gas formation which requires venting. This is generally 1% of the volume.