Fouling of Heat Exchangers

A, 5A, and 13X zeoHtes are the predorninant adsorbents for CO2 removal by temperature-swing processes. The air fed to an air separation plant must be H2O- and C02-ftee to prevent fouling of heat exchangers at cryogenic temperatures 13X is typically used here. Another appHcation for 4A-type zeoHte is for CO2 removal from baseload and peak-shaving natural gas Hquefaction faciHties. 

Although many commercial crystallizers operate with some form of selective crystal removal, such devices can be difficult to operate because of fouling of heat exchanger surfaces or blinding of screens. In addition, several investigations identify interactions between classified fines and course product removal as causes of cycling of a crystal size distribution (7). Often such behavior can be rninirnized or even eliminated by increasing the fines removal rate (63,64). 

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. 

Garrett-Price, B. A. (1985) Fouling of Heat Exchangers characteristics, costs, prevention control and removal (Noyes). 

Adaptive controllers can be usefully applied because most processes are nonlinear (Section 7.16) and common controller design criteria (Section 7.12) are based on linear models. Due to process non-linearities, the controller parameters required to give the desired response of the controlled variable change as the process steady state alters. Furthermore, the characteristics of many processes vary with time, e.g. due to catalyst decay, fouling of heat exchangers, etc. This leads to a deterioration in the performance of controllers designed upon a linear basis. 

There are three chapters in this volume of Advances in Chemical Engineering. The chapter, Analysis and Synthesis of Resilient Heat Exchanger Networks by Colberg and Morari of Caltech, is concerned with the development of new generic tools. It provides an overview on the macroscale design of systems that are resilient and flexible to uncertainties and variations in system variables, such as flow rates and fouling of heat exchanger surfaces. 

Although many commercial crystallizers operate with some form of selective crystal removal, such devices can be difficult to operate because of fouling of heat-exchanger... 

Problems with batch pyrolysis plants are often mechanical in nature and are related to residue extraction problems, coking/fouling of heat exchanging surfaces, corrosion by... 

Fouling of heat exchangers—the accumulation of deposits on their heat-transfer surfaces over a period of time—results in a degradation of thermal performance, accompanied by an increase in operating costs. 

The fouling of heat exchanger surfaces can be a major problem with solid biomass fuels, especially straws and herbaceous residues. Fouling occurs because of formation in the conversion zone of low-fusion point alkali metal salt... 

As alluded to in Chapter 8, the ideal biomass feedstock for thermal conversion, whether it be combustion, gasification, or a combination of both, is one that contains low or zero levels of elements such as nitrogen, sulfur, or chlorine, which can form undesirable pollutants and acids that cause corrosion, and no mineral elements that can form inorganic ash and particulates. Ash formation, especially from alkali metals such as potassium and sodium, can lead to fouling of heat exchange surfaces and erosion of turbine blades, in the case of power production systems that use gas turbines, and cause efficiency losses and plant upsets. In addition to undesirable emissions that form acids (SOx), sulfur can... 

Bott, T.R. Fouling of heat exchangers. 26 Chemical Engineering Monographs Elsevier Amsterdam, Holland, 1995. 

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