Operating labor requirements

H. E. Wessel [Chem. Eng., 59, 209-210 (July 1952)] made a study of the operating-labor requirements in the United States chemical... 

Operating labor requirements for chemical process industries. 

Example 6 Estimation of labor requirements. Consider a highly automated processing plant having a capacity of 100 tons/day of product and requiring principal processing steps of heat transfer, reaction, and distillation. What are the average operating labor requirements for an annual operation of 300 days ... 

Solution. The process plant is considered to require three process steps. From Fig. 6-8, for a capacity of 100 tons product/day, the highly automated process plant requires 33 employee-hours/day/processing step. Thus, for 300 days annual operation, operating labor required = (3X33X300) = 29,700 employee-hours/year. 

Operating labor also depends on the the plant capacity, m, in kg/h. Table 2.4 shows that the ejqxinent, b, in Equation 2.1 depends on the plant capacity. The exponent is 0.76 if the plant capacity is less than 5670 kg/h (12500 Ibdi) and 0.84 if it is greater than 5670 kg/h. The economy of scale is evident in Equation 2.1, because the operating labor required to produce a kilogram of product decreases as the plant capacity increases. As shown in Table 2.1, once we calculate the operating labor we can calculate the operating supervision and maintenance labor. 

Table 17.3 Direct Operating Labor Requirements for Chemical Processing Plants Basis Plant with Automatic Controls and 10-100 Ton/Day of Product...

The technique used to estimate operating labor requirements is based on data obtained from five chemical conpanies and correlated by Alkayat and Gerrard [4]. According to this method, the operating labor requirement for chemical processing plants is given by Equation 8.3 ... 

Estimate the operating labor requirement and costs for the toluene hydrodealkylation facility shown in Figures 1.3 and 1.5. 

Table E8.2 Results for the Estimation of Operating Labor Requirements for the Toluene Hydrodealkylation Process Using the Equipment Module Approach...

Economic Considerations. The principal economic consideration is, of course, total installed system cost, including the initial cost of the flow primary, flow secondary, and related ancillary equipment as well as material and labor required for installation. Other typical considerations are operating costs and the requirements for scheduled maintenance. An economic factor of increasing importance is the cost of disposal at the end of normal flow meter service life. This may involve meter decontamination if hazardous fluids have been measured. 

Operating Labor The cost of operating labor is the second largest item of expense in the manufac turing cost. Labor requirements for a process can be estimated from an intelhgent study of the equipment flow sheet, paying careful attention to the various primaiy process steps such as frac tionation, filtration, etc. The hourly wage rate should be that currently paid in the company. Once the number of persons reqiiired per shift has been estimated for a particular production rate, the annual labor cost and the labor cost per unit of production can be estimated. 

Payroh overhead includes the cost of pensions, holidays, sick pay, etc., and is normally between 15 and 20 percent of the operating-l or cost. Laboratoiy work is required for product quality control, and its cost is approximately 10 to 20 percent of the operating-labor cost. 

From this information it is possible to prepare bar charts by using a 4-week month and noting on the chart the interdependence of the various functions. The starting time for each class of work is fixed on the chart, and the duration is calciilated from the labor-hours allocated to that work from the control estimate. Work should progress smoothly as time elapses, but the operations must be linked by the order of necessaiy precedence. Starting times for the various items of work will be staggered as drawings are released and also to smooth out labor requirements. 

Operating Costs Power cost for a continuous thickener is an almost insignificant item. For example, a unit thickener 60 m (200 ft) in diameter with a torque rating of 1.0 MN-m (8.8 Mlbf in) will normally require 12 kW (16 hp). The low power consumption is due to the very slow rotative speeds. Normally, a mechanism vi l be designed for a peripheral speed of about 9 m/min (0.5 ft/s), which corresponds to only 3 r/h for a 60-m (200-ft) unit. This low speed also means veiy low maintenance costs. Operating labor is low because little attention is normally required after initial operation has balanced the feed and underflow. If chemicals are required for flocculation, the chemical cost frequently dwarfs all other operating costs. 

The advantages of the tubular filter are that it uses an easily replaced filter medium, its filtration cycle can be interrupted and the shell can be emptied of prefilt at any time without loss of the cake, the cake is readily recoverable in dry form, and the inside of the filter is conveniently accessible. There is also no unfiltered heel. Disadvantages are the necessity and attendant labor requirements of emptying by hand and replacing the filter media and the tendency for neavy solids to settle out in the header chamber. Applications are as a scavenger filter to remove fines not removed in a prior-filtration stage with a different land of equipment, to handle the runoff from other filters, and in semiworks and small-plant operations in which the filter s size, versatility, and cleanliness recommend it. 

For estimating filtration rate (therefore, operating pressure and size of the filter), washing characteristics, and other important features, small-scale tests such as the leaf or pressure bomb tests described earlier are usually essential. In the conduct and interpretation of such tests, and for advice on labor requirements, maintenance schedule, and selection of accessory equipment the assistance of a dependable equipment vendor is advisable. 

Operating Labor Centrifuges run the gamut from completely manual control to fully automated operation. For the former, one operator can run sever centrifuges, depending on their type and the apphcation. Fully automatic centrifuges usually require little dirert operation attention. 

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