Plant efficiency, overall

Paskall (25) has recently reviewed the various modifications to the Claus process that result in optimum sulfur recovery efficiency. Overall plant conversion efficiencies in the range of 97% were considered to be the upper limit at the beginning of the 1970 s (26). While this is a very respectable conversion efficiency for an industrial process the unrecovered 3% in a 2,000 tonne/d sulfur plant represents 60 tonnes/d of sulfur lost, mainly to atmosphere as 120 tonnes/d of SO2. Modifications to the four stage Claus converter train however, can raise overall conversions to over 98.5% thus halving the sulfur loss to the plant tail gas. This either reduces environmental impact or the load on tail gas desulfurization units that will be discussed later. 

Newby et al. found that increasing the PO turbine pressure resulted in higher steam flow (for a given pinch point temperature difference in the HRSG), increased PO turbine power and overall plant efficiency. However, at the highest pressure of 100 bar attempts to increase the steam flow further resulted in incomplete combustion in the main combustor and the overall thermal efficiency did not increase substantially at this pressure level. 

For land-based gas turbines, the overall plant output, efficiency, emissions, and reliability are the important variables. In a gas turbine, the processes of compression, combustion, and expansion do not occur in a single component, as they do in a diesel engine. They occur in components that can be developed separately. Therefore, other technologies and components can be added as needed to the basic components, or entirely new components can be substituted. 

After a simulation-based design of an efficient pipeless plant had been performed, the existing standard multipurpose plant was modelled by a reference model and compared to the pipeless plant setup by determining the overall production time for different production plans. 

The aim of process design is to build the best overall plant, all units within the designed plant may not operate at maximum efficiency or full potential. It is necessary to achieve a balance between the conflicting requirements of the individual units to produce the best plant possible. Plant design is an exercise in compromise and optimization. 

Fuel alcohol production could well expand further if government policies provide incentives for more widespread use as automotive fuel, and if technical developments continue to lower alcohol manufacturing costs. Some efficiency has occurred in overall plant operating costs due to seasonal balancing of the production of HFS and fuel alcohol. Plant capacity used in producing HFS for surging summer soft drink demands can be used during other times to produce fuel alcohol. 

The relations between energy efficiency and capital cost must be evaluated from the analysis of the overall plant system. At some point, improved energy efficiency will require more investment. However, many of the practical processes of today may well be operating quite far from this point. Further process analysis along these lines may well be fruitful, particularly for grass roots design situations. 

The stability and controllability of direct coupling of the PV generator with the battery, electrolyser and fuel cell have been thoroughly investigated in the PHOEBUS facility. It was concluded that the efficiency of the overall plant could be improved from 54% to 65% and an appreciable reduction in construction costs may also be expected by the omission of the converters (Schucan, 2000). 

Figure 18. Sulfur-cycle overall plant efficiency vs. cell voltage...

A comparison of the effect of the various cycles on the overall thermal efficiency is shown in Fig. 29-40. The most effective cycle is the Brayton-Ranldne (combined) cycle. This cycle has tremendous potential in power plants and in the process industries where steam turbines are in use in many areas. The initial cost of the combined cycle is between 800- 1200 per kW while that of a simple cycle is about 300- 600 per kW. Repowering of existing steam plants by adding gas turbines can improve tne overall plant efficiency of an existing steam turbine plant by as much as 3 to 4 percentage points. 

The plant has been commissioned and the first results on the performance are expected soon. Design data give an efficiency to power of 23 and 27 % respectively for extraction and condensation mode of operation while the overall plant efficiency is 73 and 39 % respectively. 

University offers many programs in this field, from subroutines to major computational systems. Chemical engineers utilize computers to develop more thermodynamically efficient procedures and to consolidate overall plant operations, especially in the areas of energy consumption, reaction rates, and hazardous waste problems. 

In the shift conversion step, carbon monoxide reacts with steam to form equivalent amounts of hydrogen and carbon dioxide. Upon cooling of the effluent gas, most of the unreacted steam is condensed and separated as process condensate. Modem ammonia plants utilize a two-step, in-series shifting, carried out at high and then low temperatures to increase conversion efficiency. Use of the dual-shift conversion system lowers overall plant steam requirements, and the lower CO leakage results in reduction in plant feed requirements due to more complete conversion of CO to hydrogen. Under normal operating conditions there is no emission from the shift converters. 

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