Pinch method

In ancient times, clay was used for food and water container construction. Civilizations in the Middle East understood the techniques of ceramics as early as 5,000 B.C. The first ceramic vessels were made by pinching. In addition to containers, small figurines were molded. The pinching method did not allow large item construction. Slab construction, rolling clay into a sheet so the clay could be cut in pieces, opened the door for crafting a wide variety of objects. 

The introduction of multiple stream splits is often cited as a drawback of the pinch method. Stream splits can be problematic in process operation. For example, when an oil or other multicomponent stream is heated and partially vaporized, then the stream is a two-phase mixture. It is difficult to control the splitting of such streams to give the required flow rate in each branch. Experienced designers usually constrain the network to avoid multiple stream splits whenever possible, even if this leads to designs that have higher than minimum utility consumption. 

Hydrogen is today a major product because its large-scale application in refining and from the perspective of fuel cells for the automotive industry. Hydrogen Pinch method has been developed to optimise the use and production of hydrogen in the context of integrated sites (Chapter 11). 

Similarly to heat saving, a water-pinch method has been developed to rationalise the recycling of process water and optimise the load of wastewater treatment. 

It is not trivial to determine the best modification options that could feature minimal capital cost and the smallest effect on existing infrastructure and thus achieve maximum energy savings. The search for such options could be very time consuming for a complex heat recovery system. The incentives to find practical yet optimal modifications have been discussed by many other researchers and practitioners. The network pinch method developed by Zhu and Asante (1999) has been proven successful for practical applications, which will be discussed in detail in this chapter. 

In the past, the retrofit methods based on the proeess pineh concept was widely used (Tjoe and Linnhoff, 1986 Policy etal., 1990 Shokoya and Kotjabasakis, 1991). However, the process pinch is developed for grassroots design and is fundamentally irrelevant to the retrofit scenario. The method (Zhu and Asante, 1999) to be discussed here is a two-stage approach identify the network pinch, the true bottleneck of an existing heat recovery system, and determine modihcations with minimum capital costs to overcome the network pinch— that is the reason why this method is called the network pinch method. 

The rationale of the network pinch method is based on the effort and difficulty required for each assessment task. The effort for conducting a revamp study is demanding as it could involve weeks or up to months depending on the complexity of the process. During the revamp evaluation stage, not only itemized costs need to be determined, but effects on piping, pressure drops, and operation will be evaluated as well. To reduce the manpower effort, the network pinch method has been implemented into mathematical... 

In the initial phase of the study, the benchmarking assessment (see Chapter 3) was applied leading to the selection of 17 major process units for a more detailed study. Application of the network pinch method enabled the identification of many opportunities within a 3 month period of the study. The study identified 73 energy modifications, with a cumulative operating cost reduction of 61.3MM/year. The... 

Columns with Intermediate Inputs and Outputs of Heat Pinch Method 173... 

Liquid flows saltatory increases or decreases in the points of intermediate output or input of heat at the temperature 7 and The minimum possible value of hquid flows at parts from column ends to the points of intermediate input and output of heat is equal to the value of liquid flow at partially reversible process in those cross-sections, where Trev = T n rev = Calculation of reversible distillation trajectory at parts from column ends to points Sr and Ss determines the function L v =f l/T) for these parts and then determines such optimal values opt and opt 7, at which summary cost of inputs and outputs energy is minimum. Such an approach was introduced in the work (Terranova Westerberg, 1989 Dhole Linnhoff, 1993) and was named pinch method. ... 

Therefore, the conceptual calculation of infinite column with intermediate input and/or output of heat consists in two stages (1) calculation of minimum reflux mode for adiabatic column, and (2) determination of opt 7, opt opt 7, and opt < 5, ( pinch method ). 

Ratios of the flow rates of liquid and vapor in two-section colunms are determined by reasoning from the calculated mode of minimum reflux and specified set of values of reflux excess coefficients, taking into consideration the output of heat by pumparounds decreasing the vapor flow rate passing from one two-section column into another. The amount of heat withdrawn by pumparounds is determined through application of the pinch method (Liebmann et al., 1998). 

Steam stripping, and a mixed variant is determined from economic considerations by means of construction of temperature-enthalpy curves for heat sources and heat sinks (pinch method). 

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