We have 250 ton water at 32°f.
We have to give it steam pressure of 5kg per cm². We have to bring it till 90°c, 100°c and 110°c. So, how much steam consumption will be to bring it at 90°c, 100°c and 110°c.
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Answers
Answer:
By analysing the heat output on an item of plant using heat transfer equations, it may be possible to obtain an estimate for the steam consumption. Although heat transfer is not an exact science and there may be many unknown variables, it is possible to utilise previous experimental data from similar applications. The results acquired using this method are usually accurate enough for most purposes.
Measurement
Steam consumption may be determined by direct measurement, using flowmetering equipment. This will provide relatively accurate data on the steam consumption for an existing plant. However, for a plant which is still at the design stage, or is not up and running, this method is of little use.
Thermal rating
The thermal rating (or design rating) is often displayed on the name-plate of an individual item of plant, as provided by the manufacturers. These ratings usually express the anticipated heat output in kW, but the steam consumption required in kg/h will depend on the recommended steam pressure.
A change in any parameter which may alter the anticipated heat output, means that the thermal (design) rating and the connected load (actual steam consumption) will not be the same. The manufacturer’s rating is an indication of the ideal capacity of an item and does not necessarily equate to the connected load.
CALCULATION
In most cases, the heat in steam is required to do two things:
1) To produce a change in temperature in the product, that is providing a ‘heating up’ component
2) To maintain the product temperature as heat is lost by natural causes or by design, that is providing a ‘heat loss’ component.
In any heating process, the ‘heating up’ component will decrease as the product temperature rises, and the differential temperature between the heating coil and the product reduces. However, the heat loss component will increase as the product temperature rises and more heat is lost to the environment from the vessel or pipework.
The total heat demand at any time is the sum of these two components.
The equation used to establish the amount of heat required to raise the temperature of a substance (Equation 2.1.4, from module 2), can be developed to apply to a range of heat transfer processes.
In its original form this equation can be used to determine a total amount of heat energy over the whole process. However, in its current form, it does not take into account the rate of heat transfer. To establish the rates of heat transfer, the various types of heat exchange application can be divided into two broad categories:
Non-flow type applications
where the product being heated is a fixed mass and a single batch within the confines of a vessel.
Flow type applications
where a heated fluid constantly flows over the heat transfer surface
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