Category: Case Study
Industry: Chemical Industry
Industry Subsector: Pigment Manufacturing
The Air XD was utilised in the pigment manufacturing industry where many of the substances, in particular – cadmium – are subject to low workplace exposure limits (WEL). Particulate matter concentrations were found as well as process leaks that previously were not noticed in an efficient or timely manner, leading to the loss of product.
The pigment industry faces challenges of maintaining product yield whilst also maintaining high standards in work place safety. Many of the substances used in the pigment industry are subject to low workplace exposure limits (WEL) making reliable and repeatable control of the manufacturing process critical. Profitability of the business is also dependent on optimisation of process efficiency.
Cadmium pigment is one of the most controlled products under REACH legislation. Cadmium products currently have a long-term exposure limit of just 25 µg/m3 as an eight-hour time weighted average (TWA). This is under review and is likely to be reduced to as little as 4 µg/m3 in the next few years.
In most companies occupational health monitoring takes the form of personal monitoring carried out every 6 or 12 months. Workers wear a personal device containing a pump connected to a filter to collect the particulate matter they would be exposed to during a typical 8-hour shift. This is then taken to a lab to analyse, the total particulate exposure along with composition analysis is generally performed to give indications of exposure to individual elements such as cadmium. This is a good way of ensuring the exposure does not exceed current limits but cannot give information about the source of the exposure. This lack of information prevents the problem from being fixed in the future and does not allow process improvement.
One of the controls used to limit worker exposure at many sites is to limit the amount of time workers spend in the production environment. This is achieved using remote process control and monitoring systems but can mean that process leaks are not noticed in an efficient or timely leading to loss of product.
Cadmium pigment manufacture involves several process steps whereby the constituent chemicals are mixed, converted to a precipitate, filtered and the resulting press cake calcined at high temperature to produce a stable pigment powder. This powder is then milled and packaged by weight for sale to manufacturers of plastics, paints, ceramics and glass.
In some companies the production process is automated to limit worker exposure whilst other sites choose to use more manual processes.
The Air XD was used in a mobile configuration mounted on a tripod. This enabled the Air XD to be moved around the production plant to monitor the active process. The aim of the deployment was to monitor the levels of airborne particulate as well as monitoring for process leaks and variation.
Figure 1: Live PM4.25 signal for pigment production area
The Air XD allows customers to track the normal particulate generated as part of the production process. Figure 1 shows the real time respirable particulate measurements during a production run. This is typical of a pigment manufacturing process with low levels of background particulate and spikes which occur when powdered products are added to the process. What the plot demonstrates is that while the process does lead to raised levels of airborne particulate, these are quickly cleared by the extraction system in the room. This is typical of a process and extraction system that are working correctly to limit potential worker exposure. This information can be used to identify the biggest contributors to airborne particulate from the process allowing these to be reviewed.
Figure 2 (Left) PM4.25 Live Signal. (Right) PM4.25 5 minute average
The benefit of the AIR XD is that it can be used to quickly identify any deviation from normal operation in real time. Figure 2 (left) shows the live signal from a process leak that occurred during cadmium pigment production. This led to a large amount of particulate matter being released into the air which could not be quickly removed by the extraction system. This was detected by the user defined 5-minute average Figure 2 (right) and triggered an alarm notifying the process controller so that the system could be shut down minimising the amount of product lost. The 5-minute average was used for the alarm trigger to prevent the alarm from being triggered by instantaneous spikes generated when products are added to the process. Only sustained raised levels of airborne particulate will trigger the alarm.
The Air XD integrates with existing process and dust control measures to allow much tighter control of the pigment production process. This brings two key benefits: