Variable speed pumps

The following types of devices are commonly applied to measure the various operational parameters of thickeners and clarifiers. They have been used in conjunction with automatic valves and variable-speed pumps to achieve automatic operation as well as to simply provide local or remote indications. 

Table 16 describes the predicted performance of the GSHP system. Total amount of extracted heat from the ground reaches 180 GJ and electricity consumption is 13.9 MWh. In this time COP ofthe heat pump unit is 4.4. When this system will adopt a constant—speed pump which can cover the maximum heat output, SCOP is 2.7. This result suggests that a variable speed pump according to the heat loads is effective to improve SCOP. On the other hand, released heat into the ground during summer is 56 GJ and the electricity of 3.6 MWh is consumed to circulate the brine between U-tubes in the foundation piles and ventilation units. SCOP during summer is estimated to be 5.7. This can be also improved. 

Variable speed pumps shall operate over their specified speed range without exceeding the vibration Umits of this standard. 

It operates by the principle of differential pumping, using a series of peristaltic pumps, each of which operates under similar conditions. The pump tubing used on each pump is the same, and the variable-speed pump with which the initial dilution is provided wiU normally pump at full speed with the same flow rate as the other two pumps. The variable speed pump is set to operate at, for example, 80% of the fixed speed pumps. Diluent is... 

Variable-speed pumps shall be designed for excursions to trip speed without damage. 

NOTE 2 The 10% differential pressure margin is intended to accommodate head increases (5.1.6), higher speed in variable-speed pumps (5.1.7) and head (testing) tolerance (see 7.3.S.4). 

Fig. 1.5.1 Schematic diagram of the falling film aerosol generator. (A) Constant-temperature oil bath (B) and (C) reservoirs containing the reactant liquid (D) and (J) glass joints controlling the flow of the moving film (E) and (F) tubes to the variable-speed pump (G) exit tube (I) boiler lube (K) carrier gas (laden with nuclei) entrance. (From Ref. 31.)...

I Install a variable-speed pump immediately downstream of the separator but upstream of the level-control valves. 

Figure 14.13. Towers with reciprocating trays or with pulsing action, (a) Assembly of a 36 in. Karr reciprocating tray column (Chem. Pro. Co.), (b) Sieve trays used in reciprocating trays columns (left) large opening trays for the Karr column (middle) countermotion trays with cutouts (right) countermotion trays with downpipes for heavy phase, (c) Rotary valve pulsator, consisting of a variable speed pump and a rotary valve that alternately links the column with pairs of suction and discharge vessels, (d) Sieve tray tower with a pneumatic pulser [Proc. Int. Solv. Extr. Conf. 2, 1571 (1974)]. (e) A pulser with a cam-operated bellows.

The control valve is a variable restriction in a pipeline which receives its position command from a controller—either in the form of a single loop regulator or as part of a more complex control system. As such, the control valve constitutes by far the most common final control element although increasing use is being made of variable speed pumps and fluidics(64) to control the flowrates of process fluids. 

Therefore, in connection with flow control system design, the first decision is whether control valves or variable-speed pumps should be used. In case of the second, flow is reduced by reducing the speed, and therefore, instead of the valve burning up the unnecessarily introduced pump head, that energy is not introduced in the first place. This reduces the operating cost of the process, but increases the capital investment, because the cost difference between variable and constant-speed pumps is usually more than the cost of control valves. 

The controls of both the "open" and the "closed" direct systems are very simple, because they consist of only a differential thermostat and a pump. The differential thermostat starts and stops a constant-speed pump whenever the detected temperature difference is favorable. In more sophisticated systems, it adjusts the speed of variable-speed pumps (or selects a small or a larger constant-speed pump for operation). What AT is "favorable" is a function of not only the "availability" of free cooling or free heating, but also of the cost of pump operation, which increases the AT thermostat set point. 

Here, a variable-speed pump transfers the hot water from the production well into the steam separator. The speed of the pump is set by the tank level. (Variable-speed pump station controls are discussed in Section 2.17). The level control signal is corrected for steam pressure variations by multiplying the two. This is called a two-element feedwater system. 

In order to maximize electrolyzer efficiency, the available solar energy has to be equally distributed by the power controller (PoC-2) among the cell electrodes and the rate of electrolyte circulation has to be matched to the electrolyzer loading. The other contribution to efficiency is minimizing pumping costs, which is achieved by the use of variable-speed pumps and by circulating only as much electrolyte as the power distribution controller (PoC-2) requires to maximize efficiency. 

Figure 2.120 shows a three-dimensional plot—(a) pressure, (b) flow, and (c) speed—where the system curves form one surface (surface A) and the pump curves form another surface (surface B). The intersection of surfaces A and B is the operating line of the variable-speed pump. 

The shape of the system curve determines the saving potentials of using variable-speed pumps. All system head curves are parabolas, but they differ in steepness and in the ratio of their static head to friction drop. The value of variable-speed pumping increases as the system head curve becomes steeper. Therefore, in mostly friction systems, the savings will be greater. 

The variable speed pump operates on the line where the surface formed by the system curves intersects with the surface formed by the pump curves. 

Optimization controls of a pump station consisting of a constant- and variable-speed pump. 

Illustration of a control system that optimizes the energy consumption of a pumping station, consisting of two variable-speed pumps, by keeping the most-open user valve at near 90% opening. 

The pump station consists of two variable-speed pumps. When only one pump is in operation and the output of PC-01 approaches 100%, PSH-03 is actuated and the second pump is started. When both pumps are in operation and the flow drops to 90% of the capacity of a single pump, the second pump is stopped if this condition lasts longer than the setting of TD-04. The purpose of the time delay (TD-04) is to make sure that the pump is not started and stopped too often. 

The savings generated by variable-speed pumping increase as the load drops off. 

If the liquid electrolyte design is selected for the electrolyzer, the optimization controls in Figure 4.1 (gatefold) include the electrolyte balancing controls based on the valve position control (VPC-32) of the variable-speed pumping station (VP-6). These controls are the same as those described for VP-1 and elaborated on in Chapter 2, Section 2.17.2. The power distribution controller (PoC-15) serves to control the electric power sent to the electrodes of the electrolyzer, and the pressure controller PC-14 serves to maintain the H2 pressure in the distribution header at around 3 bar (45 psig). 

Sophisticated gradient makers capable of generating complex gradients are now on the market (e.g. LKB). The simplest ones to operate generate the gradient using two variable speed pumps and two buffer reservoirs. The pump speeds are automatically controlled by the device so that the gradient follows any pre-determined curve. One other type, which has been used in this field and can be fairly simply constructed is shown in Fig. 4.4. A number, maybe 9, of... 

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