Desalination Capital cost

The performance ratio of ME plants is just slightly lower than the number of effects, which is deterrnined as an optimized compromise between energy efficiency and capital cost. Six effects ate typical, although plants with as many as 18 effects have been built. Eurther detail about ME desalination can be found in (56,59). 

Capital Costs A typical medium-scale RO seawater plant might produce 0.25 mVs (6 MGD). For a plant with an open sea intake, seawater salinity of 38 g/1, and conversion of 45 percent, the overall cost woiild be 26.5 miUiou (1996). A capital breakdown is given in Table 22-18. Capital charges are site specific, and are sensitive to the salinity of the feed. A plant of this size would likely contain six trains. For seawater RO, the Best estimate for the slopes of the family of lines in Fig. 22-55 is —0.6 for the equipment and 0.95 for the membranes. Capital charges, shown in TaBle 22-19, usually dominate the overall economics the numbers presented are only an example. Seawater economics are based on Shields and Moch, Am. Desalination Assn. Conf. Monterey CA (1996). 

For a certain plant capacity, the required membrane area is directly proportional to the feed water concentration. This is illustrated in Figure 12. For brackish water of ca. 3(XX) ppm TdS and an average current density of 12 mA/cm, the required membrane area for a plant capacity of 1 m product per day is ca. 0.4 m of cation- and anion-exchange membrane. Other items such as pumps, electric power supplies, etc. depend on plant size. For desalination of brackish water with a salinity of ca. 3000 ppm the total capital costs for a plant with a capacity of 1000 m /d will be in the range of US 200,000.- to US 300,000.-. The costs of the actual membrane is less than 30 % of the total capital costs. Assuming a useful life of 5 years for the membranes and 10 years for the rest of the equipment, a feed water salinity of 3000 ppm and a 24-hours operating day, the total amortization of the... 

Characterization of uncertainties in the operation and economies of the proposed seawater desalination plant in the Gaza Strip was made by using a Bayesian belief network (BBN) approach [80]. In particular, the model was used to (1) characterize the different uncertainties involved in the RO process, (2) optimize the RO process reliability and cost, and (3) study how uncertainty in unit capital cost, unit operation and maintenance (O M) cost, and permeate quality was related to different input variables. The minimum specific capital cost was found to be 0.224 0.064 US /m, and the minimum O M cost was found to be 0.59 0.11 US /m. This unit cost was for a production capacity of 140,000 mVday. 

The application of MVC for treating industrial wastewater was discussed earfrer in the chapter. Mechanical vapour compression systems are small distillation units with a capacity in the range of 250-3000 m /d [14]. Although they are small, expensive and energy-intensive units, they are often used to desalinate high salinity water, e.g., seawater and river estuary water in remote areas. In order to reduce the capital cost and energy consumption, RO-MVC hybrid systems provide a less expensive option ... 

Based on the comparison performed, reverse osmosis appears to be the most attractive seawater desalination process for desalination co-located with a MASLWR plant because of its lowest capital cost and the highest MASLWR net power supplied to the electrical grid. 

Process Turbine exhaust pressure (Pcia) Power needs (kWh/kGal) Desalination power required (MW) MASLWR power loss (MW) Net power to grid (MW) Plant production (MGal/day ) Capital cost (M ) Annual power cost (M )... 

Let s make the example more realistic. Let s assume you first need to purchase the desalinator, which costs 440,(X)0. Expenses for equipment are capital costs, not operating costs. As such, the expense of purchasing the desalinator is not included in Eq. (3.88) and thus does not affect the profit. But when we bought the desalinator. 

Test your ability to analyze process economics. Consider an alternative scheme that reduces the cost of labor but increases the capital cost. Assume that one employee can operate three desalinators. Also assume that the space you are renting on the pier can accommodate three desalinators. Calculate the profit and return on investment of purchasing three desalinators and operating for one 9-hour shift per day, 365 days per year. Although the worker is there for 9 hours a day, the desalinators are running for only 8 hours a day - it takes time to start up and shut down each day. We calculate a profit of 80,802 /year and a substantially reduced return on investment of 6%. 

As illustrated by our analysis of the desalinator, the profitability of a process is a balance between capital costs and operating costs. Capital costs are the expenses of building. The chief capital costs, in approximate order of appearance when building a chemical process, are the costs to... 

In addition to calculating the expenses of a complete process, one can also calculate the economic impact of modifying a process. Consider the precooler we added to the desalinator, shown in Figures 3.24 and 3.29. The precooler saves energy and thus lowers operating cost, but it requires an additional capital cost. Is a precooler justified economically Let s apply mathematical modeling to compare the two options no precooler and precooler. 

Figure 7.10 Cost breakdown for seawater desalination with ultrafiltration pietieatment (a) Total life-cycle cost ( indicates a capital cost) and (b) energy cost (total 3.46 kWh/m ).

Lorain, O., B. Hersant, F. Persin, A. Grasmick, N. Brunard, and J. M. Espenan. 2007. Ultrafiltration membrane pre-treatment benefits for reverse osmosis process in seawater desalting. Quantification in terms of capital investment cost and operating cost reduction. Desalination 203 277-285. 

Figure 10.4 presents an estimated cost breakdown of desalinated water produced in a typical plant. The main component is, of course, the capital and financial cost, comprised of the cost of the main equipment items feed tanks, pretreatment filtration units, pumps, pressure exchangers and piping, controls, membranes and membranes housing, post-treatment and product tanks. 

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