Rotary screw compressor

Volumetric efficiency is determined by the tip leakage past the rotors, not unlike the rotary screw compressor. The leakage is referred to as slip. 

The reciprocating, centrifugal and rotary-screw compressors described in the chapter covering this equipment design and selection are also used in refrigerant service. Sev-... 

The rotary screw compressor is designed for a specific compression ratio, (i.e., discharge pressure divided by intake pressure). If the pressure rises on the system into... 

Figure 12-110D. Rotor set for oil-free rotary screw compressor. (Used by permission Bui. CCB-0057-3-295. A C Compressor Corporation.)...

The typical rotary screw compressor stage is made up of two rotating shafts, or screws. One is a female rotor and the other a male rotor. These two rotating components turn counter to one another (counterrotating). The two rotating elements are designed so that as they rotate opposite to one another their respective helix forms intermesh (see Figure 3-78). As with all rotary compressors, there are no valves. The gas is sucked into the inlet post and is squeezed between the male and female... 

Most rotary screw compressors use lubricating oil within the compression space. This oil is injected into the compression space and recovered, cooled, and recirculated. The lubricating oil has several functions... 

There are versions of the rotary screw compressor that utilize water injection (rather than oil). The water accomplishes the same purposes as the oil, but the air delivered in these machines is oil-free. 

Some screw compressors have been designed to operate with an entirely oil-free compression space. Since the rotating elements of the compressor need not touch each other or the housing, lubrication can be eliminated. However, such rotary screw compressor designs require timing gears. These machines can deliver totally oil-free, water-free dry air (or gas). 

Detailed calculations regarding the design of the rotary screw compressor are beyond the scope of this handbook. Additional details can be found in other references [4,25,26,27]. 

The recommendations of the International Standards Organization (ISO) covering mineral-oil lubricants for reciprocating compressors are set out in ISO DP 6521, under the ISO-L-DAA and ISO-L-DAB classifications. These cover applications wherever air-discharge temperature are, respectively, below and above 160°C (329°F). For mineral-oil lubricants used in oil-flooded rotary-screw compressors the classifications ISO-L-DAG and DAH cover applications where temperatures are, respectively, below 100°C (212°F) and in the 100-110°C range. For more severe applications, where synthetic lubricants might be used, the ISO-L-DAC and DAJ specifications cover both reciprocating and oil-flooded rotary-screw requirements. 

Rotary-screw compressor mineral oils oxidation resistance is assessed in a modified Pneurop oxidation test using iron naphthenate catalyst at 120°C (250°F)... 

The aeration requirements of the deep shaft (vertical shaft bioreactor using flotation technology) are provided by two, 100 hp rotary screw compressors rated at a pressure of 7 kg/m2 (100 psig). Dissolved oxygen (DO) levels of 4 mg/L are maintained in the head tank, and during the startup phase of the plant a DO meter measured a dissolved oxygen concentration of 25 mg/L at the shaft bottom. 

For the general purpose of minimizing air flow, transport velocity, wear and power, the fluidized dense-phase mode of flow is preferred for long-distance applications. Efficient blow tank feeders, rotary-screw compressors, refrigerated dryers and stepped-diameter pipelines also are recommended. For products that are not suited to fluidized dense-phase, the possible modes of flow include dilute-phase (suspension flow) or bypass conveying (Wypych, 1995a). 

Compressed air. Oil-free compressed air is produced in rotary screw compressors. It is stored in a stainless steel receiver, then passes through a l- im filter for particle removal and two air dryers to assure complete removal of moisture traces. It is delivered to the plant via a stainless steel loop that supplies all use points and has a filter and regulator. 

Injection System. An air compressor is used to force air into the air injection wells. The compressor must be capable of injecting air at a proper flow rate under suitable air pressure. The number of wells that are fed by a given compressor also dictates the size of the air compressor. Typically, reciprocating or rotary screw compressors are used during field application (Marley et al., 1992a). Regardless of what type is used, the compressor must be oil-free in order to prevent the delivery of additional contamination to the subsurface (Johnson et al., 1993). 

Install adequate storage with intermediate pressure control for applications where air demand is variable and single-stage rotary screw compressors with load/no-load control are not fully blowing down during periods of low air demand. 

For variable air-demand systems, replace single-stage rotary screw compressors equipped with inlet-valve modulation control (or other control types [load/no-load, turn valve, etc.] not efficiently following load variations) with variable-frequency drive or reluctance-motor-drive air compressors. 

Generally, a longer element life can be expected if the air is compressed by a reciprocating compressor. Sliding vane and rotary screw compressors have a high oil carryover so that a shorter element life can be expected. In a rotary screw compressor, the bulk of the aerosol droplets measure between 0.1 and 0.5 pm. It is therefore advisable to fit a sub-micrometre filter if oil is to be separated from the compressed air effectively. The internal oil separator is intended to minimize oil carryover into the air stream. In the event of separator failure, large quantities of oil will be released, causing, in some cases, immediate failure of the filter element. 

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