Blowers and Compressors

The air supply is provided either by blowers or compressors. The difference between these components is the pressure level provided. While compressors can achieve elevated pressures up to 10 bar or higher when designed with multiple stages, low power blowers are usually hmited to fractions of a mbar. However, high pressure blowers do exist, which are able to achieve a supply pressure of 20 mbar or even up to several hundred mbar. This higher pressure is achieved by higher rotation speed and is accompanied by an increased power demand. 

Some simplified equations are provided below for the estimation of the power consumption of compressors and blowers. 

The power demand of a blower may be calculated by a simplified equation, according to Liu et al. [445]  

Blowers on a larger scale can also provide much higher pressures. Clark and Arner reported on the development of a radial blower designed for a pressure build-up of 800 mbar at flow rate of 2 m min, which worked with an extremely high speed of 150000rpm [563]. 

The power demand of an isothermal compressor (Pcomp) can be calculated according to the following formula  

The equipment size factor for a fan is the actual cubic feet per minute, ACFM, entering the fan. Fans are usually driven by an electric motor with either a direct drive or a belt. Base 

Fan Type Flow Rate (ACFM) Total Head (in. H2O) 

The head factor, Fh, for total heads greater than 4 in. H2O is given in Table 16.24. 

The brake horsepower for a fan may be computed in any of three ways, depending on whether the total change in head is mostly dynamic, static, or a mixture of the two. The corresponding nominal fan efficiency, iqf, is 40% for mostly a dynamic change, 60% for mostly a static change, and 70% for a mixture of the two. The power consumption is given by the following equation, which is similar to Eq. (16.16) and where the electric motor efficiency, can be taken as 90%  

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The affinity laws express the relationship between the head, capacity, speed, and size of centrifugal blowers and compressors. In general these relations can be applied to inlet volume conditions for good preliminary designs, but all final designs apply these laws to the actual discharge volumes from the impeller. ... 

Sliding vane, rotary blowers and compressors 346 --------- vacuum pumps 365... 

Fans, blowers, and compressors are essentially gas pumps. Fans are centrifugal machines that produce a pressure drop of less than 60 in H20 (0.15 kg/cm2). Blowers operate to about 30 psig (3.0 kg/cm2). Compressors can produce pressure up to 45,000 psig (3,000 kg/cm2). The purpose of all these items is to increase the pressure... 

The key to smooth operation of a CFB system is the effective control of the solids recirculation rate to the riser. The solids flow control device serves two major functions, namely, sealing riser gas flow to the downcomer and controlling solids circulation rate. Both mechanical valves or feeders (see Figs. 10.1(a) and (d)) and nonmechanical valves (see Figs. 10.1(b) and (c)) are used to perform these functions. Typical mechanical valves are rotary, screw, butterfly, and sliding valves. Nonmechanical valves include L-valves, J-valves (see Chapter 8), V-valves, seal pots, and their variations. Blowers and compressors are commonly used as the gas suppliers. Operating characteristics of these gas suppliers which are directly associated with the dynamics and instability of the riser operation must be considered (see 10.3.3.2). 

The key parameters to be controlled in this sub-system are air mass flow rate and pressure. Therefore, this section is focused on the characteristics of devices capable to realize useful pressure and flow rate of the oxidant feed (blowers and compressors), postponing the discussion about the integration of air supply system with the other FCS sub-systems to the successive three sections, which are dedicated to thermal and water management strategies and to overall system performance optimization. 

Fluids are moved through pipe, equipment, or the ambient atmosphere by pumps, fans, blowers, and compressors. Such devices increase the mechanical energy of the fluid. The energy increase may be used to increase the velocity, the pressure, or the elevation of the fluid. In the special case of liquid metals energy may be... 

From the standpoint of fluid mechanics the phenomena occurring in these devices can be classified under the usual headings of incompressible and compressible flow. In pumps and fans the density of the fluid does not change appreciably, and in discussing them, incompressible-flow theory is adequate. In blowers and compressors the density increase is too great to justify the simplifying assumption of constant density, and compressible-flow theory is required. 

BLOWERS AND COMPRESSORS. When the pressure on a compressible fluid is increased adiabatically, the temperature of the fluid also increases. The temperature rise has a number of disadvantages. Because the specific volume of the fluid increases with temperature, the work required to compress a pound of fluid is larger than if the compression were isothermal. Excessive temperatures lead to problems with lubricants, stuffing boxes, and materials of construction. The fluid may be one that cannot tolerate high temperatures without decomposing. 

EQUATIONS FOR BLOWERS AND COMPRESSORS. Because of the change in density during compressible flow, the integral form of the Bernoulli equation is inadequate. Equation (4.32), however, can be written differentially and used to relate the shaft work to the differential change in pressure head. In blowers and compressors the mechanical, kinetic, and potential energies do not change appreciably, and the velocity and static-head terms can be dropped. Also, on the assumption that the compressor is frictionless, / = 1.0 and hf 0. With these simplifications, Eq. (4.32) becomes... 

Since steam jets can handle large volumes of low-density vapor, thermal recompression is better suited than mechanical recompression to vacuum evaporation. Jets are cheaper and easier to maintain than blowers and compressors. The chief disadvantages of thermal recompression are the low efficiency of the jets and lack of flexibility in the system toward changed operating conditions. 

Centrifugal fans, blowers, and compressors are widely used in chemical processes because they produce a continuous flow, are relatively small, and are free of vibration. Because gases are compressible, the temperature difference between the compressed gas and the feed gas is significant at even moderate compression ratios and may limit the compression ratio possible in a single stage. However, the need for multiple stages in centrifugal compressors is usually dictated instead by impellor rotation-rate limitations, which limit the compression ratio that can be achieved. 

Air blower and compressor (positive displacement type) are preferable with silencer-cum-filter, dampers for primary (atomising) air, primary and secondary air piping, manometer, pressure regulators for air supply at burner inlet. The positive displacement-type combustion air blowers shall also be able to atomise the oil or separate compressors for atomisation of oil shall be provided. 

The various machineries for smooth conveying of sohd materials are helt, screw and bucket conveyors, hoists, overhead cranes, and fluid transf equipments such as pumps of various types, air blowers, and compressors. Many different types of processing reactor, filters, agitated vessels, condensers, gas absorbers, etc., are also required. 

The amount of CO2 deposited per unit of bed volume is an important indicator of the required capital costs, while the calculated specific cooling duty gives a good indication of the energy requirements for different cases. Blowers and compressors are responsible for part of the power consumption. The techno-economic evaluation described in the following sections includes these requirements and discusses the economic feasibility of the newly developed process concept. 

During the past five decades, gas-solids hydrodynamics studies principally have concentrated on solids phase measurements and characterization and have largely ignored the gas phase. Pneumatic conveying is an example solids are the commodity of interest the gas phase is only important in the sense that power requirements for blowers and compressors should be minimized. In studies of bubbling and turbulent fluidized beds, experimentalists study the spatial and temporal distribution of bubbles, but, typically, they employ solids measurement devices from which gas phase hydrodynamics are inferred. Circulating fluidized bed researchers also have devoted considerable attention to the solids phase, but since 1988 only 40 publications have appeared that deal with gas phase hydrodynamics. 

Rotary blowers and compressors are machines of the positive-displacement type and are essentially constant-volume flow-rate machines with variable discharge pressure. Changing the speed will change the volume flow rate. Details of construction of the various types (PI) vary considerably and pressures up to about 1000 kPa can be obtained, depending on the type. 

In blowers and compressors pressure changes are large and compressible flow occurs. Since the density changes markedly, the mechanical-energy-balance equation must be written in differential form and then integrated to obtain the work of compression. In... 

It is suggested that a user not operate a blower or a compressor near its upper limit in order to prevent it from being burned. Long-time use near the upper limit should definitely be avoided. Many blowers and compressors have temperature- or current-protection mechanisms. When the temperature or the current exceeds the preset limit, the blower or compressor will automatically shut down. 

Parasitic power loss is due to the power needs of some fuel cell components, such as sensors, control boards, pumps, fans, blowers (or compressors), solenoid valves, and switches, and due to the power losses when currents pass through certain components such as the diodes and wires. Typically, the sensors, the control boards, the solenoid valves, the switches, the diodes, and the wires consume very little power. The pump for driving the liquid coolant does not consume too much power either. It is the fans (or blowers and compressors) that consume most of the parasitic power. For an air-cooled stack, the total parasitic power loss can be controlled to less than 5% of the stack output power, and for a liquid-cooled stack, the total parasitic power loss can be controlled to less than 10% of the stack output power. 

The devices sending air to the stack can be fans, blowers, or compressors. They must meet two requirements (1) being able to send enough air to the stack for reaction (typically 2.5 to 3.0 times stoichiometric ratio), (2) being able to overcome the pressure drop caused by the stack. Fans can only be used for air-cooled stacks because their pressure boost is lower than several kPa. The advantages of fans are that they have the lowest power consumption and noise levels. Blowers and compressors are used for liquid-cooled stacks. Compressors have the highest power consumption and noise levels. Whenever possible, blowers should be used over compressors. A blower can achieve a pressure boost up to about 25 kPa. When the pressure need is more than a blower can provide, a compressor must be used. 

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