Compressors high-pressure

Many of the features of the Kellogg process, for example, centrifugal compressors, high-pressure steam systems, and high-pressure reforming, have subsequently been widely adopted by the ammonia industry. 

The peak power net can be achieved with both a blower (low pressure) and a compressor (high pressure), but the required fuel cell stack sizes are different. For the same peak P et of 86 kW, 16.3% more operating PEM cells were needed in the stack for the blower application (500 vs. 430 cells with a constant active area of 490 cm ). The blower system was able to obtain the same net power by operating just above ambient pressure at the stack and providing sufficiently higher air mass flow rates compared to that of the compressor for much of the Pnet range. 

Next it is desired to raise the pressure of the liquid, which is accomplished using a compressor. High-pressure water exits the compressor in state 4. The work required to compress the liquid is given by ... 

Pressure. High pressure gives greater solubility of solute in the liquid. However, high pressure tends to be expensive to create, since this can require a gas compressor. Thus there is an optimal pressure. 

Sometimes it is extremely difficult to avoid vapor recycles without using very high pressures or very low levels of refrigeration, in which case we must accept the expense of a recycle compressor. However, when synthesizing the separation and recycle configuration, vapor recycles should be avoided, if possible, and liquid recycles used instead. 

Injection gas pressures are usually much higher than lift-gas or gas pipeline pressures and special care has to be taken to select compressor lubricants that will not dissolve in high pressure gas. Such a situation could lead to inadequate lubrication and may impair well injectivity. 

This reduction in permeabiUty due to cake consoHdation or coUapse may be so large that it may nullify or even overtake the advantage of using high pressures in the first place and there is then no reason for using the generally more expensive pressure filtration hardware. While a simple Hquid pump may be cheaper than the vacuum pump needed with vacuum filters, if air displacement dewatering is to foUow filtration in pressure filters, an air compressor has to be used and is expensive. 

However, some of the mote important techniques in high pressure engineering which made possible the increase in throughput of reciprocating compressors from 4-5 t/h at a pressure of 125 MPa (18,000 psi) in the eady 1950s to 120 t/h at a pressure of 350 MPa (51,000 psi) can be considered. 

Dual-Pressure Process. Dual-pressure processes have a medium pressure (ca 0.3—0.6 MPa) front end for ammonia oxidation and a high pressure (1.1—1.5 MPa) tail end for absorption. Some older plants still use atmospheric pressure for ammonia conversion. Compared to high monopressure plants, the lower oxidation pressure improves ammonia yield and catalyst performance. Platinum losses are significantiy lower and production mns are extended by a longer catalyst life. Reduced pressure also results in weaker nitric acid condensate from the cooler condenser, which helps to improve absorber performance. Due to the spHt in operating conditions, the dual-pressure process requires a specialized stainless steel NO compressor. 

Recycle and Polymer Collection. Due to the incomplete conversion of monomer to polymer, it is necessary to incorporate a system for the recovery and recycling of the unreacted monomer. Both tubular and autoclave reactors have similar recycle systems (Fig. 1). The high pressure separator partitions most of the polymers from the unreacted monomer. The separator overhead stream, composed of monomer and a trace of low molecular weight polymer, enters a series of coolers and separators where both the reaction heat and waxy polymers are removed. Subsequendy, this stream is combined with fresh as well as recycled monomers from the low pressure separator together they supply feed to the secondary compressor. 

The steam balance in the plant shown in Figure 2 enables all pumps and blowers to be turbine-driven by high pressure steam from the boiler. The low pressure exhaust system is used in the reboiler of the recovery system and the condensate returns to the boiler. Although there is generally some excess power capacity in the high pressure steam for driving other equipment, eg, compressors in the carbon dioxide Hquefaction plant, all the steam produced by the boiler is condensed in the recovery system. This provides a weU-balanced plant ia which few external utiUties are required and combustion conditions can be controlled to maintain efficient operation. 

---