Variable costs estimation

The capital cost estimates are generated by the Engineering function, often based on 50/50 estimates (equal probability of cost overrun and underrun). It is recommended that the operating expenditure is estimated based on the specific activities estimated during the field lifetime (e.g. number of workovers, number of replacement items, cost of forecast manpower requirements). In the absence of this detail it is common, though often inaccurate, to assume that the opex will be composed of two elements fixed opex and variable opex. 

The business plan needs to provide projections of aimual production. Based on those estimates and assumed food conversion rates (food conversion is calculated by determining the amount of feed consumed by the animals for each kilogram of weight gain), an estimate of feed costs can be made. For many aquaculture ventures, between 40 and 50% of the variable costs involved in aquaculture can be attributed to feed. 

Budgeted income statements are identical in form to ac tual income statements. However, the budgeted numbers are objectives rather than achievements. Budgetary models based on mathematical equations are increasingly being used. These may be used to determine rapidly the effect of changes in variables. Variance analysis is discussed in the treatment of manufacturing-cost estimation. 

Utilities are very expensive and highly variable from plant to plant. Great care must be exercised to get the proper steam and electrical loads, not only in the process areas, but also in the offsite areas to make sure the cost estimate for the utilities is complete. 

Effective planning is again the key. We need to keep in mind that proper decontamination can be costly, but improper decontamination can be even more costly. One large but variable cost is the time it takes workers to decontaminate. The time that decontamination will take should be estimated and incorporated into the budget. In addition, contamination control and decontamination strategies and procedures should be outlined in the safety plan, communicated to workers, and implemented before any worker enters any area where there is a potential to become contaminated. 

These models, however, can be useful if estimates are to be made of operating costs. By assigning fixed and variable costs to each activity, average and marginal unit costs at each stage of the process can be easily calculated, which will assist in decisions regarding pricing policies or whether to buy in components and materials or make them on site. ATPLAN is an example of a network-based model of this type. 

Operating costs are conveniently considered in two groups, fixed and variable costs those dependent on production rate and those that are independent of production rate. Operating costs can be further broken down into a number of key elements as indicated in Table 14.1, where estimation guidelines for continuous plant are also given [42]. Of critical interest in the present context is how these values vary between a batch and a continuous plant of nominally the same production rate. 

In this section the components of the fixed and variable costs are discussed and methods given for their estimation. 

A simulation is a mathematical approximation of a system. The simulation of a reactor tells how the output changes with the changing input and the system variables. Simulations have at least as many constraints placed on them as cost estimates. 

The estimation of operating and capital costs is an important facet of process design and optimization. In the absence of firm bids or valid historical records, you can locate charts, tables, and equations that provide cost estimates from a wide variety of sources based on given values of the design variables. 

Sample Allocation for Estimating Concentration Levels. The variable cost of a sampling program that produces an estimate with variance given in equation (3) is... 

A pilot-scale demonstration remediating harbor sediment was conducted 1 year before the SITE demonstration. Based on the pilot-scale demonstration, the processing costs for a fuU-scale, 110-ton/day unit were projected to be 230/ton (September 1992 U.S. dollars). It is assumed that the unit will be down approximately 30% of the time for maintenance and design improvements in the first year of operation. Based on this system availability, 28,105 tons can be processed in one year. This cost included estimates for variable costs, fixed costs, and deprecia-tion/insurance. Variable costs include diesel fuel for a mobile generator, hydrogen, and caustic. Fixed costs include labor diesel fuel for pumps, heaters, process equipment, and instrumentation propane, water and sewer and parts and supplies. Depreciation/insurance costs include capital cost depreciated over a 3-year period, general insurance costs, and pollution liabihty insurance. This analysis does not include costs for setup and demobilization (D128007, pp. 5.12-5.14). 

The vendor states that BIO-INTEGRATION is not a one-size-fits-all protocol (site-specific treatability studies are required to establish the necessary treatment). Thus, treatment cost estimates are highly variable, ranging from 20 to 75 per ton of contaminated soil treated. These estimates include the cost of installation and demobilization. The vendor states that the amount and type of contaminant has little to do with costing. Factors listed as having the greatest impact on cost are ... 

The EPA s estimate for the Carver-Greenfield process assnmed treatment of 23,000 ton of drilling mud contaminate with petrolenm wastes. The total cost estimate was 523/wet ton, with 221/ton allocated to technology costs. Site costs were estimated to be 302/ton, including 240/ton for incineration of contaminated residnals. This estimate did not include regulatory, permitting, and analytical costs becanse of their variability (D11243W, p. 5.4). 

Whatever dimensionality the data have, they must be easily accessible and put to use. The data are imperative for product release, setting of product specifications that are based on true process variability, investigation of out-of-specification product, validation of the process, and trend analysis of production.28 A cost-estimate of the inefficient use of data for decision-making in a typical pharmaceutical plant shows the impact of such behavior on the company s costs. For a single product the annual costs are estimated as ... 

The scope of the economic evaluation includes estimation of capital cost figures for a nitric add plant producing 280 tonnes/day of a 60% product. Following this capital cost estimation the total annual operating costs are estimated, both variable and fixed components being considered. Also considered is the cost of providing finance for the initial capital outlay at 25% interest per annum. 

Estimated Variable Costs of Operating a 40 Million-Gal Ethanol Facility... 

Total variable cost includes the net feedstock cost plus the estimated variable cost of 0.479/gal of ethanol, from Table 3. 

Total cost includes the total variable cost plus the estimated fixed cost of 0.11/gal of ethanol. 

This estimate pertains to the case in which the DG is not dried. The total variable cost and the total cost will be higher by 0.12/gal if the DG is dried. 

These estimates are somewhat higher than the estimated variable cost of 0.392/gal for a 40 million-gal dry-mill plant provided by Whims (13) and the average cash operating cost of 0.417/gal for dry mills reported in a survey of ethanol producers for 1998 (14). The difference is owing primarily to the higher cost of natural gas in California at the time we prepared our estimates. The prices of natural gas we use are explained in Table 3. 

Operational costs include fixed and variable costs per year. The following items have been assessed maintenance, which is the main contributor, labour and raw materials. Energy costs are not considered in this study. Maintenance is estimated with ratio of capital investment for chemical... 

Cost Estimation. The capital costing equations used in the cogeneration problem have been designed to yield approximate capital and maintenance expenditures and to reflect the consequence of changing the system s variables on these costs. The form of these equations expresses equipment costs in terms of stream and performance variables. In all cases a capital recovery factor is used to account for the cost of capital (i = 15%) and estimated useful life (n = 40 years). 

The equations of constraint link the cost estimate through the system s thermodynamic performance to fuel costs. The thermodynamic analysis must relate the variables used to describe the system s performance to those used in the cost estimate. In this problem, costing equations are used which are generally in terms of stream and performance variables. Thus the thermodynamic analysis need only be in terms of these variables. Sixteen equations of constraint have been developed from a thermodynamic analysis of the cycle, and are given in Table III. 

The solution procedure requires the designer to select a feasible set of decision variables y for the first iteration. Once this initial set of five decision variables has been chosen, the entire design (for that iteration) is fixed and the set of state variables x, and cost estimates are determined. With values assigned to all the state and decision variables, the set of shadow prices SP(i), is evaluated, and in turn, the set of marginal prices, PM(i), is determined. These marginal prices are then used to direct the iteration as described by Equation 16. 

The solution to the problem is obtained by solving mass and energy balances to yield the quantity and state (i.e., composition, temperature, pressure) of all the streams and the utility requirements. Additional parameters for the process equipment, sufficient so that stream specifications are met and the cost of the equipment can be estimated, are calculated. The cost of equipment, raw materials, and utilities is estimated and an economic analysis is carried out. Methods of cost estimation and economic analysis are presented later in this text. This entire procedure may be repeated many times to examine modifications of the process flow sheet or to find optimal values of key process variables. Computer software can greatly simplify these repetitive calculations for the engineer. But even without the need for repetition, the software may simplify the calculations and provide detail and accuracy that would have been impossible otherwise. 

The individual steps and cost estimations may be somewhat lengthy, as indicated in Section 4.4, but are well within the power of a digital computer. The major difficulty in a problem of this kind is that a function of (m + 1) variables has to be calculated, stored and interpolated. A device that is sometimes used to overcome this... 

An additional complication in formulating the objective function is the quantification of uncertainty. Economic objective functions are generally very sensitive to the prices used for feeds, raw materials, and energy, and also to estimates of project capital cost. These costs and prices are forecasts or estimates and are usually subject to substantial error. Cost estimation and price forecasting are discussed in Sections 6.3 and 6.4. There may also be uncertainty in the decision variables, either from variation in the plant inputs, variations introduced by unsteady plant operation, or imprecision in the design data and the constraint equations. Optimization under uncertainty is a specialized subject in its own right and is beyond the scope of this book. See Chapter 5 of Diwekar (2003) for a good introduction to the subject. 

Variable costs can usually be reduced by more efficient design or operation of the plant. Methods for estimating variable costs are discussed in Section 6.4. 

The transportation of product to the user is a widely variable cost element. A power plant located at the minehead-processing plant site would have eflFectively no transportation cost. Rail transport of solid product would probably experience the same costs as coal itself (2). This can be estimated in lieu of specific foreknowledge of rail rate schedules through 1990 as per ton-mile. As an example of current costs to ship coal, low sulfur Western coal was shipped recently to New Jersey for utility use at a cost of 22 per ton, which corresponds closely to per ton-mile. 

Based on cost/performanee of the preferred eomposition and emrent products, identify a recommended selling price for the new product. Considering all available factors, identify the market share that may be expected at the recommended selling price. Making reasonable estimates, identify the expected variable costs and fixed costs associated with the new product. Identify the market share required for break-even, and compare to the expected market share to determine if the new product is likely to be profitable on an ongoing basis. Calculate the net profit expected on an ongoing basis. 

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