Minimum full flow rate

Minimum full flow rate Storage system cost g/skW /kWh net 0.02 To be determined 0.02 0.02... 

If turndown is desired, the grid pressure drop criteria (Eqs. 3 and 4) should apply at the minimum gas flow rate. This can be a problem for circulating fluidized bed combustors, since this means that under full load the grid pressure drop will be unacceptably high. Also, if the grid is curved, i.e., concave, convex, or conical, the criterion must apply with respect to the lowest hole on the grid. Take an example of a fluid bed with curved grid, as shown in Fig. 3. 

In establishing specifications, the first important items to identify from the plant process material balance are normal, maximum, and minimum intake or suction flow rates together with corresponding conditions of temperature and pressure. The required discharge pressure must be established. If it is necessary or important to be able to operate at reduced or over-normal flow rates, these should be identified for the manufacturer, together with the length of time of such expected condition e.g., full time at one-half rate, 20 minutes out of every hour at 10% over normal, etc. These operating requirements may separate the types of equipment. Because it is uneconomical to purchase horsepower that cannot be used by the fluid system, ask that the manufacturer state the maximum load and/or conditions that will fully load the available horsepower of the compressor-driver unit. 

A special condition called slack flow can occur when the gravitational driving force exceeds the full pipe friction loss, such as when a liquid is being pumped up and down over hilly terrain. Consider the situation shown in Fig. 7-5, in which the pump upstream provides the driving force to move the liquid up the hill at a flow rate of Q. Since gravity works against the flow on the uphill side and aids the flow on the downhill side, the job of the pump is to get the fluid to the top of the hill. The minimum pressure is at point 2 at the top of the hill, and the flow rate (Q) is determined by the balance between the pump head (Hp = — w/g) and the frictional and gravitational resistance to flow on the uphill side (i.e., the Bernoulli equation applied from point 1 to point 2) ... 

Under the particular feed conditions and element arrangement for this test, the criteria of less than 3.5% C02 in the residual stream could not be reached without experiencing some loss in separation efficiency. This goal could be achieved, however, by operating at higher flow rates with more elements in series. The conclusion arrived at from these data, therefore, is that there is a critical minimum flow rate for given feed gas conditions and element array. In order to maximize system performance this parameter must be taken into consideration when designing a full size system. 

The process variable to be controlled, PV that is, any stream- or operation-related variable in the flowsheet (e.g., pressure, temperature, liquid level, species mass or mole fraction, mass or molar flow rate). In addition, the minimum and maximum values of the PV are used to express the PV as a percentage of its full range ... 

The controller output, OP, to be manipulated by the controller, as a percentage of its full range. This variable is usually either a stream flow rate or the rate of heat transfer of an energy stream. Grenerally, its minimum value is specified as zero and its maximum is taken as twice its nominal value. Note that occasionally the nominal value is not positioned midway between the minimum and maximum values (e.g., when the nominal flow rate of a bypass stream lies near its maximum or minimum flow rate). 

The operators, concentrating their attention on the fact that the level in the pressurizer was higher than normal, were erroneously convinced that the primary system was full of water and that therefore the core was safe. They, unfortunately, made, at this point and later in the course of the accident, some fatal manoeuvres, all consistent, however, with this erroneous conviction of theirs. One of the operators, about two and a half minutes after the start of the HPI pumps, stopped one of them and reduced the water flow rate of the other to a minimum. Subsequently a controlled spillage of the primary water was started. During the subsequent inquiries, he said The rapidly growing pressurizer level at the start of the accident made me believe that the high pressure injection (HPI) was excessive and that soon we would have the primary system completely full of water . 

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