Optimum cleaning time

The I I cleaning procedures as a whole, compared with household laundering, are characterized by huge variations in the composition of the soils, types of surface to which they adhere, cleaning time available, etc. The optimum choice of enzyme type and dosage level normally has to be established through a cooperation between the customer (end user), manufacturer of the detergent, and enzyme producer. 

For some processes, though they would not be classified as batch processes, the period of continuous production will be limited by gradual changes in process conditions such as, the deactivation of catalysts or the fouling of heat-exchange surfaces. Production will be lost during the periods when the plant is shut down for catalyst renewal or equipment clean-up, and, as with batch process, there will be an optimum cycle time to give the minimum production cost. 

During the time an evaporator is in operation, solids often deposit on the heat-transfer surfaces, forming a scale. The continuous formation of the scale causes a gradual increase in the resistance to the flow of heat and, consequently, a reduction in the rate of heat transfer and rate of evaporation if the same temperature-difference driving forces are maintained. Under these conditions, the evaporation unit must be shut down and cleaned after an optimum operation time, and the cycle is then repeated. 

The optimum boiling time given by Eq. (27) shows the operating schedule necessary to permit the maximum amount of heat transfer. All the time available for operation, emptying, cleaning, and refdling should be used. For... 

The total cost includes (1) fixed charges on the equipment and fixed overhead expenses, (2) steam, materials, and storage costs which are proportional to the amount of feed and evaporation, (3) expenses for direct labor during the actual evaporation operation, and (4) cost of cleaning. Since the size of the equipment and the amounts of feed and evaporation are fixed, the costs included in (1) and (2) are independent of the cycle time. The optimum cycle time, therefore, can be found by minimizing the sum of the costs for cleaning and for direct labor during the evaporation. 

Students can decide how to dilute the bleach to change reaction time. Halving the concentration doubles the time. Once this is established, students could test other chemicals to see how they react with the red juice extract - for example, hydrogen peroxide, other enzyme-based cleaners, etc. This would give the opportunity to investigate the best reaction conditions for optimum cleaning of a red juice spillage. 

A worked example showing how basic filtration data can be used to assess the optimum cycle time, and hence filter area required to complete a clarification of a v etable oil using precoat filtration on a pressure leaf filter. The filtration is assumed to be constant rate, after having formed a precoat of 2 mm on the pressure leaves prior to clarification. The cleaning and reforming of the precoat takes iproximately 30% of the total cycle time, hence active filtration time is only 70% of any given cycle time. The analysis is based on a 14 h working and 350 days per year. These are easily altered in cells D15 and D16, respectively. 

The term 6cc is a cost-modified value of the cleaning time constant, 6ce< which becomes equal to 0cc when K = F, but is commoniy greater than cc- The optimum throughput for a minimum cost Cycle is such that the tangent from g = (at P = 0) to the curve of P versus 6 touches the curve at (flopt. Popt )- Actual cleaning time is then O c + aPopt - The graphical solution is shown in Figure 12-2. 

Slow responding electrodes are easily rejuvenated and cleaned by dipping in warm (60 C) chromic acid cleaning solution for about two minutes. The electrodes are then exercised by dipping alternatively in hydrochloric acid (0.1 N) for about one minute and sodium hydroxide (0.1 N) for about one minute. The exercising is continued until an optimum response time is observed. The electrode is then stored in the hydrochloric acid solution before standardization. 

Checking Against Optimum Design. This attempts to answer the question whether a balance needs to be as it is. The first thing to compare against is the best current practice. Information is available ia the Hterature (13) for large-volume chemicals such as NH, CH OH, urea, and ethylene. The second step is to look for obvious violations of good practice on iadividual pieces of equipment. Examples of violations are stack temperatures > 150° C process streams > 120° C, cooled by air or water process streams > 65° C, heated by steam t/ urbine 65% reflux ratio > 1.15 times minimum and excess air > 10% on clean fuels. 

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