Plant size

The price differential at which coal becomes competitive with gas depends on plant size and the cost of capital, but based on estimates by the International Energy Agency (21) the required price ratio for gas to coal in North America falls into the range of 3.1 to 3.7 on an equivalent energy basis ( /MJ). Current prices give a gas/coal cost ratio nearer 1.5 to 2.0. As a result, all projected new methanol capacity is based on natural gas or heavy oil except for the proposed coal-based plant in China. 

Urea Process. In a further modification of the fundamental Raschig process, urea (qv) can be used in place of ammonia as the nitrogen source (114—116). This process has been operated commercially. Its principal advantage is low investment because the equipment is relatively simple. For low production levels, this process could be the most economical one. With the rapid growth in hydrazine production and increasing plant size, the urea process has lost importance, although it is reportedly being used, for example, in the People s RepubHc of China (PRC). 

In seawater—dolime and hrine—dolime processes, calcined dolomite or dolime, CaO MgO, is used as a raw material (Table 9). Dolime typically contains 58% CaO, 41% MgO, and less than 1% combined Si02, P O, and CO2 where R is a trivalent metal ion, eg, Al " or Fe " ( 4). Roughly one-half of the magnesia is provided by the magnesium salts in the seawater or brine and the other half is from dolime (75). Plant size is thus reduced using dolime and production cost is probably lower. 

Fig. 12. Costs as a function of plant size for (—) coal-fired steam plants and (-) early MHD power plants where x corresponds to the EGAS reference...

In a similar appHcation, Cape Industries has announced its intention to commission a solvent extraction plant to recover acetic acid from an effluent generated at its dimethyl terephthalate [120-61-6] faciHty (Wilmington, North Carolina) (44,45). The plant was commissioned in Eebmary 1995. In this case, the solvent will be CYANEX 923 extractant [100786-00-3], CYANEX 923 is also a phosphine oxide, but unlike TOPO is a Hquid and can be used without a diluent (46,47). This has the benefit of reducing plant size, capital, and operating costs. 

Economic Aspects. Isophthahc acid in North America sold for 1.19— 1.32/kg in 1994, depending on the shipment method. The price of xylene plays a role, although not to the same extent as -xylene in terephthaUc acid. The far lower production volumes and smaller plant sizes for isophthahc acid do not give the same economies of scale. 

Depending on energy and raw material costs, the minimum economic carbon disulfide plant size is generaHy in the range of about 2000—5000 tons per year for an electric furnace process and 15,000—20,000 tons per year for a hydrocarbon-based process. A typical charcoal—sulfur facHity produces approximately 5000 tons per year. Hydrocarbon—sulfur plants tend be on the scale of 50,000—200,000 tons per year. It is estimated that 53 carbon disulfide plants existed throughout the world in 1991 as shown in Table 2. The production capacities of known hydrocarbon—sulfur based plants are Hsted in Table 3. The United States carbon disulfide capacity dropped sharply during 1991 when Akzo Chemicals closed down a 159,000 ton per year plant at Delaware City, Delaware (126). The United States carbon disulfide industry stiH accounts for about 12% of the total worldwide instaHed capacity. 

It can be assumed that P,Jp, and for the cascade have been specified, and that the cost of feed and the cost per unit of separative work, the product of separative capacity and time, are known. The basic assumption is that the unit cost of separative work remains essentially constant for small changes ia the total plant size. The cost of the operation can then be expressed as the sum of the feed cost and cost of separative work ... 

Simulations of the lands of reaclor intended for the pilot or plant scale. Howto do the scale-up to the plant size, however, is a sizable problem in itself. 

Equation (9-208) can be used to compute data for plots such as Fig. 9-40, which shows the decrease in processing cost per unit of production ApoIRo with increasing plant size. 

FIG. 9-40 Decrease in processing cost against increase in plant size. 

As a general rule, the optimum number of effects increases with an increase in steam cost or plant size. Larger plants favor more effects, partly because they make it easier to install heat-recovery systems that increase the steam economy attainable with a given number of effects. Such recoveiy systems usually do not increase the total surface needed but do require that the heating surface be distributed between a greater number of pieces of equipment. 

Two-fluid nozzles do not operate efficiently at high capacities and consequently are not used widely on plant-size spray diyers. Their chief advantage is that they operate at relatively low pressure, the hq-uid being 0 to 400 kPa/m" pressure, while the atomizing fluid is usually no more than 700 kPa/m" pressure. The atomizing fluid may be steam or air. Two-fluid nozzles nave been employed for the dispersion of thick pastes and filter cakes not previously capable of being handled in ordinaiy atomizers [Baran, Ind. Eng. Chem., 56(10), 34-36 (1964) andTurba, Brit. Chem. Eng., 9(7), 457-460 (1964)]. 

In the plant-size unit, Fig. 18-26 must be translated into a mass-transfer-rate curve for the particiilar tank volume and operating condition selected. Every time a new physical condition is selected, a different cui ve similar to that of Fig. 18-27 is obtained. 

Seleetion of a tail gas expander depends on the temperature and pressure on the inlet eonditions of the nitrous gas. The pressure equals that of the eompressor outlet minus the pressure losses in the eyele. Depending on proeess and plant size, these losses amount to 0.3-2.0 bar. The inlet temperature may vary widely from plant to plant. Figure 4-19 shows an expander in the 10,000 kW power output eategory. 

Depending on plant size, the hot gas expander is supplied either with (Figure 4-40) or without variable inlet guide vanes. Adjustment features are not required in small plants where throughput at eonstant or full-load eapaeity is antieipated. 

For a fundamentally new process, plant size is a variable requiring extensive study outside the scope of this handbook. Reference 4 addresses determination of such a project s core of viability. ... 

Corrigan, T. E., and Dean, M. J. Determining Optimum Plant Size, Chemical Engineering, August 14, 1967, p. 51. 

Order of Magnitude 50% Lab. Data, Plant Size Raw Materials... 

Favorable operational economics and good management practices require high levels of control of the ozonation system. Depending on the specific process of ozone applications, plant size, and design philosophy, the control system may be simple or complex. The trend in Europe is toward highly sophisticated and centralized control. 

There are many factors to be considered in selecting the type of Powerformer to use. It largely depends on the local situation and includes such things as feed stock, octane level, the value of gasoline yield, the use for by-product hydrogen, plant size, etc. While we can not completely generalize, we can mention some of the more important considerations. 

---