The use of closed-loop piping systems in pharmaceutical processes
Most pharmaceutical organisations utilise process cooling plant as part of the manufacturing processes. The cooling water is used for tablet formation, batch processing, R&D, liquid sterilisation, ointment and cream cooling etc. In recent years, many pharmaceutical companies have opted to use closed-loop (the subject of an earlier blog post) cooling towers as opposed to open-loop systems. There are a number of reasons for this as in cooling tower systems, the continuous operation of fans and pumps makes these systems quite energy-intensive resulting in high operating costs. The systems can also suffer from solid deposits, gases, scale accumulation on heat exchangers, oxidation, microbiological growth, algae, bacteria/legionella, etc. it is, therefore, necessary to enforce suitable and costly and intensive maintenance procedures and chemical treatment to prevent these undesirable conditions arising.
Traditional cooling towers utilise evaporation to reduce the process water temperature. In the case of closed-loop sytems, the process water is cooled using ambient air. The latter system produces significant energy savings and as closed-loop systems reuse the process water, considerable reductions in water consumption is achieved. This helps pharmaceutical organisations to get closer to the required or target sustainability goals. It has been noted in published literature that, when using closed-loop process water systems in lieu of open-loop systems, companies can save up to 98% of process cooling water due to the recirculation of water around the loop.
The reuse and recirculation of the clean water also eliminates notable costs associated with consumption disposal and treatment. Further efficiencies can be achieved from the use of closed-loop processes cooling systems as in many climates, chillers can be turned off permitting free-cooling during winter months. The control system can monitor outdoor air temperature and shut down the refrigeration compressors when appropriate. These compressors are large energy consumers and as such, having the ability to shut down these units when the climate permits, saves considerable energy thus reducing operating costs. Energy reduction of up to 95% through effective implementation of such a control strategy has been quoted in published literature.
The use of variable speed fans and pumps further increase the savings through the optimised use of energy.
Many pharmaceutical sites also utilise pumped purified water loops. Whilst more modern facilities are designed to include energy efficient systems and energy saving measures, older systems can also offer energy saving opportunities. The following example from a pharmaceutical site is of an existing purified water loop system which contains a single circulation pump which provided a maximum flow rate of 56 m3/h at 8 bar pressure. The general operating demand was 40 m3/h at 8 bar pressure. The total length of the piping is approximately 246 M with a rise of approximately 25.0 M on the return leg to the tank.
It was considered by the client that the existing pump was not matched to the system and coupled with the extensive daily system operating hours, was contributing to the high system electrical costs experienced on site.
A baseline model was developed for the system and solved at a design flow rate of both 40 and 56 m3/h. Figure 1 provides an overview of the model.
Based on a design flow rate of 40 and 56 m3/h, the calculated duty pressure rise is 31.56 and 66.29 m fluid respectively.
The existing circulating pump was then assigned to the model and it was seen that the pump generated a flow rate of 61.9 m3/h with a duty pressure rise of 78.67 m fluid. This performance was based on the pump speed of 2900 rpm and an impeller diameter of 255mm. The duty power requirement under this operation was 24kW. Figure 2 provides an overview of this simulation. Reducing this pump speed to 2656 RPM reduced the flow rate to 56 m3/h. The associated power requirement was 18.4 kW.
A proposed alternative pump as put forward by a pump vendor was then modeled in the system (Figure 3). This pump produced a flow rate of 56 m3/h. The power required for this pump was 15.2kW. Reducing the speed of this pump to achieve a flow rate of 40 m3/h lowered the power requirement to 5.8 kW, much lower than the original pump installed in the system.
This example from a real pharmaceutical site demonstrates how energy savings can be achieved in existing purified water systems in pharmaceutical sites. Cooling water distribution as well as other utility systems can be modeled thereby identifying energy saving opportunities.
- Pharmaceutical Manufacturing.