Fresh water consumption

In order to reduce fresh-water consumption in the scrubber, the usage of distillation bottoms and the off-gas condensate should be maximized since diey have the least ammonia content. The flowrate resulting from combining these two sources (5.8 kg/s) is sufflcient to run the scrubber. However, its ammonia composition as determined by the lever-arm principle is 12 ppm, which lies outside the zone of permissible recycle to the scrubber. As shown by Fig. 4.7, the maximum flowrate of the off-gas condensate to be recycled to the scrubber is determined to be 4.1 kg/s and the flowrate of fresh water is 0.9 kg/s (5.8 — 0.8 — 4.1). Therefore, direct recycle can reduce the fresh-water consumption (and consequently the... 

As a result of segreg ion, interception and recycle, we have eliminated the use of fresh water in the scrubber leading to a reduchon of fresh water consumption (and influent to biotreatment) by 6.0kg/s. Therefore, the target for segregation, interception and recycle has been realized. Next, we focus our attention on sink/generator manipulation to remove fresh-water consumption in the steam-jet... 

So far the discussion on water minimization has restricted consideration to identify opportunities for water reuse. Maximizing water reuse minimizes both fresh water consumption and wastewater generation. However, the process constraints for inlet concentrations, outlet concentrations and flowrates have so far been fixed. Often there is freedom to change the conditions within the operation. Typical process changes that might be contemplated include ... 

III. Heat/Process Integration Study Pinch analysis is well established for finding optimal utilities, heat transfer area, optimal fresh water consumption, minimum cooling water demand, reduced emissions targets and so on (Smith, 2005 Kemp, 2007). One application of pinch analysis to retrofitting the heat exchanger network of a crude... 

Reduce waste generation instead of waste treatment. For example, waste/foul water recycle with or without treatment reduces fresh water consumption and also avoids the need to expand waste water treatment plant... 

In this chapter, the design and retrofitting of a water network are optimized for both fresh water consumption and total water flow rate at the inlet of regeneration units. 

Write down the model equations for water network involving only processes, and no regeneration units. Calculate the fresh water consumption for each process, using loads of different contaminants in each process and maximum outlet concentrations of different contaminants in water streams from each process (given Table 12.1). 

Consider a smaller refinery water network problem by ignoring some processes in Table 12.1, and perform design, retrofitting and revamping via multi-objective optimization for two objectives, namely, fresh water consumption and total flow through the regeneration units, as in this chapter. 

Here we will present a two-stage optimisation strategy for the design of water using systems which makes use of the insights provided by water pinch analysis and combines them with mathematical progranuning tools. Both capital cost and fresh water consumption are minimised. 

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