ABSTRACT

Deposits on surfaces in water - bearing systems, also known as ”fouling,” can lead to substantial losses in the performance of industrial processes as well as a decrease in product quality and asset life. Early detection and reduction of such deposits can, to a considerable extent, avoid such losses. However, most of the surfaces that become fouled, for example, in process water transport pipes, membrane systems, power plants, food and beverage industries to name a few, are difficult to access and the analysis of the water phase do not reveal the extent of the deposits. Furthermore, it is of interest to distinguish between microbiological and nonmicrobiological deposits. Although they occur together, different counter measures are necessary. Therefore, sensors are required that indicate the development of surface fouling in real time, non-destructively, in situ and can discriminate between abiotic and biotic based deposits. A new and novel sensor has been developed that provides said discriminate detection by utilizing conventional heat transfer reduction sensory coupled with ultrasonic detection of materials on the same surface concurrently. The technical aspects of the design, operation, and application will be discussed in the paper. Real time graphical detection followed by automated reduction control runs will also be presented as well as revealing if the deposit is biotic or abiotic.

INTRODUCTION

One of the main causes of performance loss, quality and runnability problems in industrial systems is related to contaminants and deposits. These deposits are composed of inorganic, organic and / or microbial matter, respectively. Most of the deposits contain various or even all types of these contaminants and form complex matrices. Of these, microbiological contaminations, also named biofouling, are one of the biggest issues and risks in water bearing industrial systems. They cannot only cause deposits that impact the function and efficiency of the systems. They often are the cause for health risks (e.g., Legionella). Fouling can be generalized into four forms, inorganic, suspended solids, organic, and microbiological. Of these forms of fouling, it is only inorganic crystallization fouling that does not lead to the worst form of corrosion, namely localized. This type of corrosion eventually transitions into high pitting penetration rates that drastically reduce the asset life.

The majority of the fouling which occurs in aqueous systems are detected indirectly by means of reduced process side throughput, increased time to get to operating temperature and or pressure, pressure drop, approach temperature increase, or the use of extensive instrumentation to calculate ”at that time” heat exchange U-coefficients and or cleanliness factors. Under certain circumstances, some of these methods are not sufficiently accurate unless normalized. Or the measurements taken have not been corrected for cooling water or process flow changes, shear stress change and bulk cooling water change or surface temperature changes. There may be a large lag time to foulant detection which can lead to foulant aging and dehydration to a point of being irreversible fouled, whereby chemistry and chemical adjustment in the water side environment would not provide cleansing of the surface and maintain a clean state. An example would be the comparative time for a side stream annular heat transfer test section to detect fouling of a well instrumented utility surface condenser, wherein they were both operated at the same surface temperature and shear stress (velocity corrected for the geometry) on the same cooling water.4 The steam surface condenser heat transfer surface area for 175 MW would be 150,000 ft2 (13,935 × 106 mm2) would require a large quantity of foulant coverage to be detected compared to the annular test section which has 0.05 ft2 (4645 mm2) of foulant detection surface.

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