Monitoring and Targeting

WASTE MINIMISATION AND THE POWDER COATING INDUSTRY

4) Improved Housekeeping

3.3 Assessment Techniques Used in the Waste Audit Step

3.3.3 Monitoring and Targeting

were developed and used to estimate flow rate settings for optimal water usage and pollutant concentration.^111142151

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Figure 3.4 An example of an XY scatter graph of consumption versus production⁸⁹¹⁵⁵ The regression line is often used to highlight several features of the process. Firstly, the y-intercept gives the baseload¹⁰⁴ of the process, which is the amount of material consumed at zero production. The slope or gradient indicates the process efficiency¹⁰⁴ of the plant: thus the smaller the slope, the higher the efficiency. Finally, the spread of the points on either side of the line gives a measure of the level of control over the process.¹⁰⁵¹⁵⁶ In this case a plot of the amount of powder used as function of product output, will be plotted, to evaluate the powder consumption. Determining the reasons for poor efficiency, process control and a high baseload enables waste minimisation opportunities to be identified. An ideal graph should have a small slope, an intercept close to zero and the data points should lie as close as possible to the regression line. At this point targeting comes into play. The regression line can be used to set a realistic target, which is the desired consumption of the resource related to production. Once drawn, the target can be set below the actual consumption if reduced consumption is required. The validity and practicality of this target should be verified using a mass balance. This type of analysis identifies the causes of the fluctuations and thus the potential sources of waste. These graphs allow various time periods to be compared.

They also show variations in performance. A target level can be included on a trend graph (see Figure 3.5).

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Figure 3.5 An example of a trend graph of consumption versus time^104,155 Monitoring the amount of water consumed is essential for any company that employs a wet pre-treatment step. A survey was carried out by Envirowise, previously called the Environmental Technology Best Practice Programme, to collect empirical data from metal finishers in the UK as part of one of the few monitoring and targeting exercises to be reported in the literature. This survey can be related to production data using the Water and Paint Economy Diagrams shown in Figures 3.7, 3.8 and 3.9. These diagrams allow companies to establish and manage their water usage more effectively.¹⁵⁷ A line was plotted through the graphed data to represent the average water consumption in relation to the surface area and mass of workpieces processed. This line served as a baseline measure of performance and was referred to as a key performance indicator.¹⁰⁴ Two 'target' lines were drawn on either side of this line, one above and one below. These lines demarcated areas on the graphs where the worst and best performances in water usage were achieved, respectively. In order to use these diagrams a company first has to measure two parameters, namely annual water usage and the number of workpieces processed during the same time period in units of m² and tonnes.¹⁵⁷ The values obtained for the above measurements can then be plotted as on Figure 3.7 to establish which of the four performance areas they fall into with respect to their water usage.

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Figure 3.7 Water economy diagrams ¹⁵⁷

A similar approach was used to evaluate how effectively companies were coating their workpieces. The amount of paint and powder consumed in the industry was plotted against thickness of the coating layer as measured after processing. The less powder 158

used to obtain the required thickness, means less powder is wasted and better performance is achieved.

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Figure 3.9 Powder waste ¹⁵⁸

Statistical Process Control (SPC) can also be thought of as a form of monitoring and targeting where one of the variables is fixed. Examples in the literature of variables which are constant include the quality of the finished product and effluent.¹⁵⁹ For products this can be specification criteria set by the client buying the finished product, in- house criteria set by the manufacturing company for work in progress,¹⁵⁹ or standards set by an independent watch dog body.¹¹²¹⁵⁹

Although there are many advantages of monitoring and targeting, these include cost savings of between 5 and 15%,¹⁵⁹ from reducing energy usage and input consumption and pinpointing the source of waste. The literature survey showed this method to be the least widely used waste minimisation technique in both industry and research.