Cooling system

The cooling systems required to remove the low- temperature process heat depend heavily on the plant location. The availability of water (wells, rivers, sea water) and the meteorological conditions are important factors for the selection of an optimum cooling system. 

Air coolers are normally used to cool down process flmds to approximately 60 °C and for condensation units operating above such temperatures. These air coolers are at least as energy-efficient as water coolers over these temperature ranges and require some 2-3 kWh per GJ of discharged heat. Temperatures are controlled either by switching fans on or off, or by closing louvers to shade some of the cooling tubes. Air coolers require considerable space. 

The cooled water is collected in a concrete basin underneath the cooling tower and pumped from there through the plant cooling systems. Since evaporation in the cooling tower consistently concentrates the salt in the cooling water, a small quantity of water - depending on the salt content of the make-up water and on the allowable salt concentration in the loop - has to be continuously withdrawn. This blowdown water and the water lost by evaporation have to be replaced by appropriately conditioned make-up water. 

Larger water rates with a small t are normally prefmed also for direct cooling with river or sea water. Provided that the flow rate is kept within a relatively narrow range, carbon steel can still be used for sea water piping whereas the coolers themselves often require expensive alloys which are not always easy to handle, for instance admiralty metal or copper/nickel alloys. 

A combination of two cooling systems may sometimes be found as well, for instance in plants which have both a number of smaller process coolers and large turbine waste steam condensers installed. Whereas the latter are operated with sea water wherever possible, the former are normally combined into a small open or closed loop. 

There are seven systems, six of which are run in a similar way and one (system No. 2) operated differently because stainless steel predominates (Table 46). Circulating flow rates vary from 1 100 to 1 300 per system. Total make up amounts to  

The concentration ratios are held at 1.4 to 1.95 for normal systems (leakage control should raise this figure to 2). The ratio is 1.2 for system No. 2, where an attempt is made not to exceed a Cl content of 50 mg l h Conditioning is done  

Continuous chlorination treatment and a biocide plus dispersing agent shock treatment are used on make up water to prevent biological growth. 

The most direct way to reject heat above ambient temperature to the environment is by the use of aircooled heat exchangers, as discussed in Chapter 151. These coolers exploit a flow of ambient air across the outside of tubes through which process fluids are flowing that require cooling. Such air coolers are very common in some industries, particularly when the plant is located in a region where water is scarce. 

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It became evident that tube and water gradually was heated up during inspection. Therefore a water cooling system was placed after the drawing matrices but before the measuring chamber. 

Metal surfaces in motion have also been characterized by STM, one of the clearest examples bemg tire surface diflfiision of gold atoms on Au(l 11) [29] (figure Bl.19.7). Surface diflfiision of adsorbates on metals can be followed [30] provided that appropriate cooling systems are available, and STM has been successfiilly employed to follow the 2D dendritic growtli of metals on metal surfaces [31]. 

Open steady-flow systems, which include almost all air conditioning processes, foUow this law. Examples include the energy flows in a cooling and dehurnidifying coil or an evaporative cooling system. 

Cooling is routinely appHed, either with ambient process water if THF is the solvent or with chilled brine if diethyl ether is used. Since Grignard reagents are particularly reactive with water, Hquid hydrocarbon coolants may be preferred, to eliminate the risk that could arise from a cooling-system leak. 

A reactor system is shown in Figure 2 to which the HAZOP procedure can be appHed. This reaction is exothermic, and a cooling system is provided to remove the excess energy of reaction. If the cooling flow is intermpted, the reactor temperature increases, leading to an increase in the reaction rate and the heat generation rate. The result could be a mnaway reaction with a subsequent increase in the vessel pressure possibly leading to a mpture of the vessel. 

Safety. A large inventory of radioactive fission products is present in any reactor fuel where the reactor has been operated for times on the order of months. In steady state, radioactive decay heat amounts to about 5% of fission heat, and continues after a reactor is shut down. If cooling is not provided, decay heat can melt fuel rods, causing release of the contents. Protection against a loss-of-coolant accident (LOCA), eg, a primary coolant pipe break, is required. Power reactors have an emergency core cooling system (ECCS) that comes into play upon initiation of a LOCA. 

Carbon produced by these latter reactions is formed in the catalyst pores, making it much more difficult to remove, and potentially causing physical breakage. Operating steam to carbon ratios are chosen above the minimum required in order to make carbon formation by these reactions thermodynamically impossible (3). Steam is another potential source of contaminants. Chemicals from the boiler feedwater or the cooling system are poisons to the reformer catalyst, so steam quality must be carefully monitored. 

Filtration and water-knockout systems are used to clean up the gas before it enters a compressor. Cooling systems are sometimes required to maintain compressor discharge temperatures below 54°C to avoid damage to the pipeline s protective coatings. Automated compressor stations are typically staffed by maintenance and repair personnel eight hours per day, five days per week. Other stations are staffed on a 24-hour basis because personnel must start, stop, and regulate compressors in response to orders from the dispatch office. 

Tetrasilver tetroxide is a powerful oxidizer for sanitizing swimming pools, hot tubs, and industrial cooling system waters (see Water, treatment of SWIMMINGPOOLS, SPAS, AND HOT tubs). This oxide is slightly soluble and its dissociation into silver ions is enhanced by the addition of the oxidizer KgSgOg. Bivalent and trivalent silver disinfectants have been shown to be from 50 to 200 times more effective as sanitizers than monovalent silver compounds. 

Cooling-Tower Plumes. An important consideration in the acceptabiHty of either a mechanical-draft or a natural-draft tower cooling system is the effect on the environment. The plume emitted by a cooling tower is seen by the surrounding community and can lead to trouble if it is a source of severe ground fog under some atmospheric conditions. The natural-draft tower is much less likely to produce fogging than is the mechanical-draft tower. Nonetheless, it is desirable to devise techniques for predicting plume trajectory and attenuation. 

Molten materials can also be cooled to soHd products on endless-belt systems, as shown in Figure 12. Some typical materials treated, product and feed characteristics, and capacities of belt cooling systems are given in Table 5. 

Table 5. Product Characteristics and Capacity Data for Some Materials Treated in Belt Cooling Systems ...

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