Steam usage

When considering the need for capital pretreatment equipment, sufficient care should be taken not to propose any particularly sophisticated external or internal water treatment regimen that of itself creates restrictive operational BW control limitations—where boiler design, steam usage, and common sense dictate no necessity for such limitations to be imposed. The overall water treatment program should not be overdesigned but should properly match the needs of the project. 

For simple HW and LP steam heating applications, employing perhaps a Scotch marine or firebox FT boiler, the water quality requirements are unlikely to be onerous, but as pressure ratings and heat-flux densities increase (and other factors such as special boiler designs and steam usage applications are taken into consideration) water quality becomes increasingly important. Thus, in general ... 

In the United States, those amines covered under 21CFR 173.310 may be used safely in the preparation of steam that contacts food, provided that the amount of additive required is not in excess of functional needs and the steam usage is not more than required to achieve the intended effect. Control limits for amines are ... 

Figure 23.30 Site profiles allow targets for steam usage and steam generation for the whole site to be developed.

Consider an example involving a site where there are four steam mains with their steam usage and generation detailed in Table 23.3. The utility system can use a gas turbine with a power output of 25 MW, if appropriate. The gas turbine is integrated with a HRSG17. 

Many caustic evaporator suppliers have schemes to separate the two types of caustic whilst making 50% solutions of both. A particularly good option is to install an extra first-effect evaporator for the membrane caustic soda and split the steam usage between the diaphragm first-effect and the new membrane first-effect, then recombine the steam again to feed to the rest of the diaphragm cell evaporator system. 

Plant capital (45,000 tons p.a. m) Steam usage (Ib/lb acetic acid) Operating cost ( /ton acetic acid)... 

Low hydrocarbon partial pressure with higher steam rate (total pressure of about 12-15 psig and steam usage of 25 wt% of the feed)... 

Site Flow Rate Feed Conc. Effluent Conc. Investment in Dollars Steam Usage (tons/year) Power Usage Service Contract in Dollars/Year... 

In a four-effect evaporator steam is put into the first effect, where an effect relates to vapor flow, and the heat from that steam is used four times before condensation occurs in a barometric condenser. In theory, a four-effect evaporator will remove four liters of water per kilogram of steam usage, but in actual practice that water removal is about 3.4 1 per kg of steam-Heat losses and the change in the heat of vaporization with temperature account for the difference. 

The authors pose the problem as a multiple objective function problem, and, in their example, consider the two competing objectives of total evaporator heat exchanger area and steam usage. The paper is really a clever way of eliminating a number of flow patterns as never being candidates for the optimal solution regardless of the relative importance of the cost for area versus steam costs. For a particular triple effect example problem, they show that, depending on the liquid feed temperature, 3,... 

Integration of steam usage in the plant for considerable savings... 

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