Stream factor

The heart of an electrolysis plant is its electrolysers. The factors that improve the Rol are features such as low energy consumption and high on-stream factors, flexibility of plant load, high current densities and short electrolyser downtime periods for maintenance. 

All these modifications lead to the fulfilment of all aspects for an improvement of the Rol by KU single element technology and high efficiency of the latest cell design, such as low energy consumption with a high on-stream factor for the plant, simple and rapid maintenance of the electrolysers, plant load flexibility and high current densities. 

This would account for a typical 3-4 week turnaround period with the remaining days representing unplanned feed outages. Extending the turnaround interval to 5 years with an improved on-stream factor of about 0.98 is a reasonable target for refiners. 

Economic analysis of costs based on pilot-scale demonstration results gave an estimated cost of 98 to 206 per ton of waste treated. 85 to 90% of these costs are for raw materials (cement and Chloranan) and labor. The lowest value ( 98 per ton) is based upon the vendor s expectation of reducing chemical consumption by 33%, attaining an on-stream factor of 90%, and using a new 2300-lb/min batch processing unit. These costs do not include profits of the... 

Eighty percent on-stream factor at 292 days per year. 

Stream factor Percentage of actual plant on-stream time compared with the possible on-steam time. 

To determine the required selling price of hydrogen, a cash flow analysis was performed using an after-tax internal rate of return (IRR) of 15%. Other major assumptions used in the analysis were equity financing for a 20 year plant life including two years of construction time, a 90% on-stream factor with 50% plant capacity in first year of production, 30% of capital investment is spent in the first year and 70% in the second year, a tax rate of 37%, and ten year straight-line depreciation. 

Table II. COMPARISON OF VARIOUS PROCESSES FOR PRODUCING 100 (90% Stream Factor Annual Costs) X 106 SCF/day HYDROGEN ...

Because of the considerable uncertainties in all the assumptions made, this projected hydrogen cost should not be rigorously compared with the cost projections we have made for the other processes discussed in this paper. Moreover, we have not reworked Knoche and Funk s economics to conform with the guidelines of Table 1. (The assumptions they made were an 80% stream factor, utility financing, 12 % capital recovery factor, and mid-1976 dollars.)... 

Sensitivity Analysis. The sensitivity of hydrogen price to the following variables was calculated raw materials cost, plant capital cost, stream factor, plant size, and by-product credits. 

Table III. SUMMARY OF CAPITAL AND OPERATING COSTS FOR PRODUCING 100 X 106 SCF/DAY OF HYDROGEN AT 300 TO 500 psig BY VARIOUS PROCESSES (Mid-1979 COST BASIS, 90% Stream Factor)...

Stream Factor Changes We assumed that for stream factors of 30%, 50%, and 70%, the raw materials requirement would be reduced proportionately, but capital-related costs do not change from the base case. We calculated the hydrogen price the same way as in the base case. 

HYDROGEN PLANT STREAM FACTOR, % of design capacity... 

Figure 10. Effect of change in stream factor on hydrogen price for 100 X 106 scf/day of hydrogen production hy various processes...

Operation for 330 days per year (90% stream factor for conventional economic analysis). However it should be emphasized that higher stream factors (>95%) are achievable depending upon reliability of oxygen supply. 

Dihydrate process maintenance costs are substantially less than those for hemi processes due to less severe process conditions. The on-stream factor is also higher for the average dihydrate facility. 

The plant operates 330 days/yr (90 percent on-stream factor). 

Ever> economic calculation requires the prior determination of an operating cost (FF year) or a cost price (FF/t of product or feed). It also presumes the prior fixing of the stream factor (theoretical operating time of a unit in a year. 8000 h year in general) and the utilization factor, which the ratio of actual output to production capacity (100 per cent in a preliminary calculation). 

An overall review of the world activity of existing units shows that they operate on the average with a high stream factor, which is around 310 days/year, and which tends to improve with increasing size. The main cause of incidents is still the synthesis compressor. but also the primary reforming step. 

An important influence on production cost has, of course, the so-called on-stream factor, the number of production days per year. It is standard practice to assume that a well designed and operated plant should be capable to reach a minimum of 330 days per year, a value on which economic calculations are usually based. Modern plants often achieve higher on-stream factors. A beneficial effect is also that many plants achieve higher capacity than the original design. Plant outages because of operational problems or temporary shut downs for economic reasons because of unfavorable market situation can lower the profitability considerable. The on-stream factor is an average value, because plants should shut down only every 2 to 3 years for a major turn-around for repair and preventive maintenance. Only a very few short unscheduled shut-downs for repair work should occur between two turn-arounds. A start up needs between 15 to 30 hours and consumes a considerable amount of natural gas without an equivalent production (100 000-200 000 DM/d). 

If the predicted corrosion rate indicates only short exposures, then the design engineer should allow for frequent inspection of the plant and periodic replacement of the affected equipment. This affects process economics in two ways, as it reduces the on-stream factor (number of days of production per year) and increases the maintenance costs. Usually the economic impact of frequent shutdown and replacement is so negative that use of a more expensive alloy with better corrosion resistance can be justified. 

As was expected, demetallation/denitrification of the feed stock was substantially lower than that for Catalyst Systems B and C. Even though product pattern with this system was superior, short catalyst cycle length and consequently limited On-Stream Factor (OSF) weighed heavily against it. Short catalyst cycle length was operationally uneconomical due to frequent shut downs. 

The plant stream factor is expected to be 90%. (The stream factor is the fraction of time that the plant operates over the course of a year.)... 

Pump B is the more economical choice. Note, however, that the difference is only about 2%. Small changes in the cost of electricity, the actual pump efficiencies, or the stream factor could shift the choice to pump A. 

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