However, in others, like tanks and vulcanisers, it may not only be important but crucial to the overall process.Ĭonsider two non-flow heating processes requiring the same amount of heat energy but different lengths of time to heat up.
In some non-flow type applications, the process heat up time is unimportant and ignored. Some processes are concerned with heating solids typical examples are tyre presses, laundry ironers, vulcanisers and autoclaves. Typical examples include hot water storage calorifiers as shown in Figure 2.6.1 and oil storage tanks where a large circular steel tank is filled with a viscous oil requiring heat before it can be pumped. A steam coil situated in the vessel, or a steam jacket around the vessel, may constitute the heating surface. In non-flow type applications the process fluid is held as a single batch within the confines of a vessel. Where a heated fluid constantly flows over the heat transfer surface. Where the product being heated is a fixed mass and a single batch within the confines of a vessel. To establish the rates of heat transfer, the various types of heat exchange application can be divided into two broad categories: However, in its current form, it does not take into account the rate of heat transfer. In its original form this equation can be used to determine a total amount of heat energy over the whole process. 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. The total heat demand at any time is the sum of these two components. 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. 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. In most cases, the heat in steam is required to do two things:ġ) To produce a change in temperature in the product, that is providing a ‘heating up’ componentĢ) To maintain the product temperature as heat is lost by natural causes or by design, that is providing a ‘heat loss’ component. The manufacturer’s rating is an indication of the ideal capacity of an item and does not necessarily equate to the connected load. 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.Ī 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 thermal rating (or design rating) is often displayed on the name-plate of an individual item of plant, as provided by the manufacturers. However, for a plant which is still at the design stage, or is not up and running, this method is of little use. This will provide relatively accurate data on the steam consumption for an existing plant. Steam consumption may be determined by direct measurement, using flowmetering equipment. The results acquired using this method are usually accurate enough for most purposes.
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 steam demand of the plant can be determined using a number of different methods:īy 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. This will enable pipe sizes to be calculated, while ancillaries such as control valves and steam traps can be sized to give the best possible results. The optimum design for a steam system will largely depend on whether the steam consumption rate has been accurately established. Including warm-up, heat losses and running loads.
Steam jet ejector design calculation spreadsheet how to#
How to calculate steam requirements for flow and non-flow applications.