On-Off Flow And Pressure Control For Parallel Pumps On-Off Flow Control For Parallel Pumps On-Off Pressure Control For Parallel Pumps

On-Off Control System For Compressors For intermittent demand, where the compressor would waste power if run continuously, the capacity can be controlled by starting and stopping the motor. This can be done manually or by the use of pressure switches. Typical switch settings are on at 140 PSIG (1 MPa), off at 175 PSIG (1.2 MPa).

Compressors and Types of compressors Compressors are gas transportation machines that perform the function of increasing the gas pressure by confinement or by kinetic energy conversion Types of compressors Centrifugal compressors. Rotary compressors. Reciprocating compressors. Centrifugal compressors. Suction throttling Discharge throttling Variable inlet guide vanes Speed control Rotary compressors. Bypassing Speed control Reciprocating compressors. On/off control Constant-speed unloading Speed control speed control and unloading

Surge Control In Compressors The design of compressor control systems is not complete without consideration of surge control, because it affects the stability of the machine. Surging begins at the positively sloped section of the compressor curve. In Figure 1 this occurs at S1 on the 100% speed curve at 4400 lbm/hr (1980 kg/hr). If the flow never drops below this limit, that will ensure safe operation for all speeds, but some power will be wasted at speeds below 100% because the surge limit decreases at reduced speed Various schemes to control surge are outlined in the following  Compressor pressure rise ( ΔP = PD−PI) vs. Differential across suction flow meter ( h). Pressure ratio (PD/PI) vs. actual volumetric flow (Q) Break horsepower vs. mass flow (m) Pressure ratio (PD/PI) vs. Mach number squared Incipient surge Surge spike detection

Compressors Series And Parallel  Compressors A compressor is a mechanical device that increases the pressure of a gas by reducing its volume. An air compressor is a specific type of gas compressor. Two compressors are in series Compressors can be connected in series to increase their discharge pressure (compression ratio) or they can be connected in parallel to increase their flow capacity. Series compressors on the same shaft can usually be protected by a single anti-surge control system. Two compressors are in parallel When operating multiple compressors in parallel, the total flow (load) can be so distributed among the machines that one is fully loaded and the other handles the variations in demand. Controlling two or more compressors operating in parallel and having identical characteristics would be relatively simple. It is very difficult, if not impossible, to find two compressors having identical performance characteristics. Slight variations in flow can cause one compressor to

On-Off Level Control In Dual Pump Station On/off switching is the most common capacity control in use. It has many disadvantages such as flow surges that often hinder processing, high friction losses, and high electricity peak demand charges. However, on/off control is simple and can be economical, as its consequences do not require redesign to accommodate the limitations of on/off control. Pumps that are controlled only by starting and stopping are said to be constant-speed (CS) pumps.

Surge Phenomenon  and Anti-Surge Phenomenon Surge Phenomenon In axial or centrifugal compressors, the phenomenon of momentary flow reversal is called surge. During surging, the compressor discharge pressure drops off and then is re established on a fast cycle. This cycling, or surging, can vary in intensity from an audible rattle to a violent shock. Intense surges are capable of causing complete destruction of compressor parts, such as blades and seals. The characteristic curves of compressors are such that at each speed they reach a maximum discharge pressure as the flow drops Surge Phenomenon In Compressors A line connecting these points (A to F) is the surge line. If flow is further reduced, the pressure generated by the compressor drops below that which is already existing in the pipe, and momentary flow reversals occur. The frequency of these oscillations is between 0.5 and 10 Hz. The surge frequency of most compressor installations in the processing industries slightly less than

Start/Stop Sequence In Pumps  When the running adjustable speed pumps are near their maximum speeds and when more flow is needed, the capacity of the pumping station must be increased by starting another pump. Similarly, when all pumps are at a low speed and less flow is needed, a pump must be stopped. It is necessary to know the maximum pump speed a pump can run at and still deliver zero flow (called omega zero, ωo), the  pressure up to which the flow remains zero (shut-off pressure). This is the pressure that a starting pump must overcome before it can start delivering flow (superimposed back-pressure), and the flow delivered by an adjustable-speed centrifugal pump, which is running against the back-pressure, which is superimposed by the other operating pumps.

End Point Detection Control In Batch Reactors One way to increase plant productivity is to reduce batch cycle time. If the reaction continues beyond the optimal endpoint, the process yield can be reduced due to side reactions. In batch reactors, if the completion of the reaction cannot be reliably detected, it is common practice to terminate reactant flow on the basis of total charge. In other reactions, the endpoint is accompanied by the fall or rise of the reaction pressure. This change in pressure can be used to have a pressure switch or pressure controller to shut off the reactant flow

End Point Detection and pH End Point Control   End Point Detection Determining reaction endpoint in polymer/resin reactors is critical to achieve desired product properties, such as molecular weight. Knowing exactly when the reaction is complete saves residence time and batch conversion time, and lowers the overall manufacturing cost. One way to increase plant productivity is to reduce batch cycle time. If the reaction continues beyond the optimal endpoint, the process yield can be reduced due to side reactions. reactions, the endpoint is accompanied by the fall or rise of the reaction pressure. This change in pressure can be used to have a pressure switch or pressure controller to shut off the reactant flow pH End Point Control   pH is used in detection the end point. pH end point control is important to realize that during most of the reaction the measurement will be away from set point. Therefore, integral action must not be used, because it would saturate and overshoot would result

Effects Of Lag The lag effect describes the likelihood that we will better recall information when time between repeated exposure to that information increases. The lag effect demonstrates that successive repetition is not the most effective way to retain information.

Time Constant The time required for a current turned into a circuit under a steady electromotive force to reach to (e-1)/e or 0.632 of its final strength (where e is the base of natural logarithms) specifically the ratio of the inductance of a circuit in henry to its resistance in ohms the relaxation time in the discharge of a capacitor that is equal to the product of the resistance in ohms of the discharging circuit and the capacity in farads of the condenser

 Reaction Rate Reaction rate, in chemistry, the speed at which a chemical reaction proceeds. It is often expressed in terms of either the concentration (amount per unit volume) of a product that is formed in a unit of time or the concentration of a reactant that is consumed in a unit of time.

Stability Of Reactors The response of a reactor to a change in temperature (i.e., the overall reactor stability) depends especially on the algebraic sign of αT. A reactor with negative αT is inherently stable to changes in its temperature and thermal power, while a reactor with positive αT is inherently unstable.

limitations of cascade control in case of reactors it requires an additional measurement (usually flow rate) to work.  there is an additional controller that has to be tuned. the control strategy is more complex – for engineers and operators Cascade control is beneficial only if the dynamics of the inner loop are fast compared to those of the outer loop. Cascade control should generally not be used if the inner loop is not at least three times faster than the outer loop, because the improved performance may not justify the added complexity.

Ratio Control Strategy For Endothermic Reactor  Ratio control is used when two fluids must be mixed together in a specific ratio. A practical way to do this is to use a standard control system to control the flow on one line. The same transmitter signal is used as a set point for a second controller which controls the flow in a second line

Fluidized Bed Dryer A high-pressure Hot air from the supply is passed through the perforated container containing a wet mass of the granules, after some time granules, particles started to suspend in the air to become dry (called (fluidized state), the process is called fluidization.

Spray Dryer A spray dryer takes a liquid stream and separates the solute or suspension as a solid and the solvent into a vapor. The solid is usually collected in a drum or cyclone. The liquid input stream is sprayed through a nozzle into a hot vapor stream and vaporized.  Spray dryers can dry a product very quickly compared to other methods of drying. They also turn a solution (or slurry) into a dried powder in a single step, which simplifies the process and improves profit margins. How spray dryer is different from other dryers Spray dryers are useful in encapsulation processes because they quickly and efficiently separate a substance into ultra-fine fragments. As opposed to methods such as freeze drying, pulse combustion drying, and drum drying, spray drying technology is very quick, inexpensive, and easy for a factory to utilize.

 Rotary Dryers Rotary dryers are very versatile process equipment as it can accommodate a large variety of products over a wide range of flow rates. To obtain a uniform product quality and to operate the dryer economically with minimal environmental impact, it is necessary to use efficient control strategies. 

Evaporation  Evaporation will be limited to concentrating aqueous solutions in a closed vessel or group of vessels Evaporation is an energy-intensive process. Its efficiency can be improved by increasing the number of evaporators in series (effects), and some of the energy can be recovered by vapor recompression Single effect evaporation A conventional evaporator is heated by steam which condenses and transmits heat energy to the solution to be evaporated. As this solution boils it in turn releases vapor which may: – Either be condensed in a condenser, in which case the process is known as “single effect” evaporation. Multiple effect evaporation In a multiple effect evaporator, water is boiled in a sequence of vessels, each of which is at a lower pressure than the last. As the boiling point of the water decreases with pressure, the vapor produced in one vessel can be used to heat the next vessel. Only the first vessel requires a source of external heat.