Open-air plants

Open-air plants are recommended because the average wind velocities are high enough to safely dilute volatile chemical leaks that may exist within a plant. Although safety precautions are always practiced to minimize leaks, accidental releases from pump seals and other potential release points. 

A plant handling substantial quantities of flammable toluene is located 1000 ft from a residential area. There is some concern that a sizable leak of flammable vapors will form a flammable cloud with subsequent ignition in the residential area. Determine the minimum mass flow rate of toluene leakage required to produce a vapor cloud in the residential area with a concentration equal to the LFL. Assume a 5 mph wind and D atmospheric stability. 

Assume a continuous leak at ground level. The plume concentration directly downwind along the cloud centerline is given by Equation 5-48  

Solving for Qm, the mass flow rate from the leak, we obtain 

The LFL for toluene is 1.4% in air (from appendix B). Converting the units, we obtain 

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Two fairly large dished head low-pressure 32-percent hydrochloric acid tanks supplied a periodic flow of acid to a chemical process in an open-air plant in the sunny southern United States. (See Figure 6—15.) The two rubber-lined, horizontal storage tanks were 12 ft. (3.7 m) in diameter and about 40 ft. (12.2 m) in length. A small vent scrubber that used water absorption for any fumes during the filling operation, served both acid tanks. 

Constmction of new power plants in the coal region of the western United States presents serious problems in states whose laws dictate zero effluent. In these plants, cooling-tower water withdrawn from rivers cannot be returned to them. In these situations, cooling-tower effluent is purified by distillation (vapor-compression plants have predominated) and by a combination of distillation and membrane technology. The converted water then is used as boiler feedwater the plant blowdown (effluent) is evaporated from open-air lined pools, and pool sediment is periodically buried back in the coal mine with the flue ashes. 

Usually, a gas turbine plant operates on open circuit , with internal combustion (Fig. 1.3). Air and fuel pass across the single control surface into the compressor and combustion chamber, respectively, and the combustion products leave the control surface after expansion through the turbine. The open circuit plant cannot be said to operate on a thermodynamic cycle however, its performance is often assessed by treating it as equivalent to a closed cyclic power plant, but care must be taken in such an approach. 

The Hawthorne and Davis analysis is first generalised for the [CBT]i open circuit plant, with fuel addition for combustion,/ per unit air flow, changing the working fluid from air in the compressor to gas products in the turbine, as indicated in Fig. 3.11. Real gas effects are present in this open gas turbine plant specific heats and their ratio are functions off and T, and allowance is also made for pressure losses. 

Fig. 6.2 shows a simplified diagram of the basic STIG plant with steam injection S per unit air flow into the combustion chamber the state points are numbered. Lloyd 2 presented a simple analysis for such a STIG plant based on heat input, work output and heat rejected (as though it were a closed cycle air and water/steam plant, with external heat supplied instead of combustion and the exhaust steam and air restored to their entry conditions by heat rejection). His analysis is adapted here to deal with an open cycle plant with a fuel input/to the combustion chamber per unit air flow, at ambient temperature To, i.e. a fuel enthalpy flux of/7i,o. For the combustion chamber, we may write... 

Most modem CCGT plants use open air cooling in the front part of the gas turbine. An exception is the GE MS9001H plant which utilises the existence of the lower steam plant to introduce steam cooling of the gas turbine. This reduces the difference between the combustion temperature T ot and the rotor inlet temperature The effect of this on the overall combined plant efficiency is discussed in Ref. [1] where it is suggested that any advantage is small. 

A similar argument can be used for a fuelled semi-closed cycle, assuming that it can be regarded as the addition of an open CBT plant and a closed CHT cycle with identical working gas mass flow rates (and small fuel air ratios). Suppose the latter receives its heat supply from the combustion chamber of the former in which the open cycle combustion takes place. If the specific heats of air and products are little different, then the work output is doubled when the two plants are added together, but the fuel supply is also approximately doubled. The efficiency of the combined semi-closed plant is, therefore, approximately the same as that of the original open cycle plant. 

The data in Figure 6-23 are valid only for TNT explosions occurring on a flat surface. For explosions occurring in the open air, well above the ground, the resulting overpressures from Figure 6-23 are multiplied by 0.5. Most explosions occurring in chemical plants are considered... 

The amount of explosion overpressure is determined by the flame speed of the explosion. Flame speed is a function of the turbulence created within the vapor cloud that is released and the level of fuel mixture within the combustible limits. Maximum flame velocities in test conditions are usually obtained in mixtures that contain slightly more fuel than is required for stoichiometric combustion. Turbulence is created by the confinement and congestion within the particular area. Modem open air explosion theories suggest that all onshore hydrocarbon process plants have enough congestion and confinement to produce vapor cloud explosions. Certainly confinement and congestion are available on most offshore production platforms to some degree. 

While the volume of concentrate can be determined based on plant capacity and recovery, the evaporation rate at any given site varies with climate. To determine the evaporation rate of fresh water at certain locations, a standard pan evaporation measurement is taken. Evaporation pans are small, open air pans filled with water from which losses in water due to evaporation are measured. Standard size Class A evaporation pans are most commonly used, which are 1.207 m in diameter and 0.25 m in depth. The daily change in depth, minus any rainfall, is used to determine the evaporation rate in mm/day. This rate takes into account the effects of climate on evaporation rate, but corrections for pond area and salinity must be made when determining the evaporation rate of a specific evaporation pond. 

In carnation plants, the half-lives of a-endosulfan stored under four different conditions, non-washed and exposed to open air, washed and exposed to open air, nonwashed and placed in an enclosed container, and under greenhouse conditions, were 6.79, 6.38, 10.45, and 4.22 d, respectively (Cefon et al., 1995). 

The first consideration is that the heat cannot escape as easily as in open air. Unless the fire is totally starved of oxygen, it would be at least as hot as the equivalent open air case whether it is a pool, spray, or jet. The action of the roof and the plant will be to cause flame recirculation. This tends to increase the depth or thickness of the flames and, thus increases the radiation. In the jet... 

Infrastructure—refrigerator plant, offgas treatment, air-conditioning systems, locker rooms, spares, and other facilities, located in the basement or as open-air installations on the roof of the plant. 

The reciprocating compressor was one of three identical units mounted side-by-side under a covered shed in an open-air chemical plant. These compressors were capable of compressing about 50 tons per day of acidic gases from 25 psig to 175 psig. The compressor operated at 300 RPM and was driven by a 150-horsepower electrical motor. This 30-year-old compressor was initially designed with a well water cooling flow on the jacket. Initially a 3/4-inch valve supplied well water. The water flowed out of the compressor jacket and into a funnel, so the operator had a visual indication of flow and no provisions to block the water. [3]... 

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