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Chill out & Scale Up!

In many pilot-plant or production facilities temperature control systems are like a wallflower at the junior high school dance – they are not the most technical, expensive or exciting equipment in the room and are easily overlooked. But, when the most popular person in the class asks the wallflower to dance, everyone notices! Likewise if a problem occurs with the temperature control system the process stops and the repair team dances into action. Actually ‘wallflower’ is a respectable moniker for a chiller; meaning that the chiller performs reliably but by no means belies its importance. 

Scaled up processes in the pilot or production scale introduce new challenges for temperature control systems. The thermodynamic profile of the process must be thoroughly known with sufficient cooling capacity to reach the desired process conditions. Typically processes incorporate a capacity safety factor of ~20-30%. Any process cooling applications using tap water should have a thorough cost analysis and environmental impact study conducted. Switching to a recirculating cooler with
automated process control and data capture systems increases efficiency and accountability. Keeping the chiller running to the manufacturer’s specifications is crucial for optimal operation and longevity.

The use of tap water for cooling purposes is common in small scale operations. However, at the pilot or production scale (>20 L) the use of tap water for cooling purposes should be avoided. Tap water temperatures fluctuate greatly throughout the year. The inability to lower temperatures when needed eliminates any capacity safety factor. This lack of cooling capacity control and consistency could lead to a reduction in process efficiency or the potential loss of production. The cost of the water supply/sewer charges weighs significantly in operating budgets. Cooling rotary evaporator condensers is a typical application of recirculating coolers. An average 3 liter rotary evaporator uses approximately 230,000 liters of cooling water per year. This corresponds to an annual water consumption of a family of four. If the annual costs for cooling water of 2,212.80 € (consumption per year 461 m3 x costs per m3 4.80 €) are compared with the running/operational costs of a recirculating cooler to the amount of 403.20 € (consumption per year 2016 kW x costs per kWh 0.20 €), this results in cost savings of 1,809.60 € per year. In addition, fresh water is a limited resource with periodic rationing in various locations. If water restrictions activate in your plant area, what do you do? As corporate “green” policies and scrutiny become publicly transparent the unnecessary waste of fresh water exudes environmental irresponsibility. Dedicated recirculating chillers eliminate the waste of fresh water, reduce operating costs and deliver reliable process control. Large capacity chillers (up to 20 kW) can control dedicated cooling processes such as condensers, packaging systems, reaction vessels and semi-conductor applications. Circulators with a large pumping capacity (80 l/min, 6 bar) can even control multiple systems when meeting the cooling requirements. Depending on the process, circulators accommodate the use of a variety of fluids for temperature control, including; water, glycols, alcohols, silicones, etc. Some of these fluids have a lower heat capacity than water allowing the chiller to cool or heat the process faster than water. More importantly chillers offer precise temperature control through a PID controller. Temperature stabilities <±1 °C deliver peace of mind that the process temperature conditions remain constant and reproducible.

The proper installation, proximity and connection of the recirculating chiller to the application is paramount in affecting the overall process performance. Cooling efficiency is affected greatly by sufficient insulation and an unhindered flow of coolant through the tubing or piping. Follow these six points to achieve the best conditions:

1) Minimize tubing length – keep the tubing as short as possible and well secured
2) Maximize thermal exchange – utilize tubing and connectors with the proper diameter; avoid bath fluid flow path restrictions
3) Insulate – install insulation on all tubing, connections and vessels to maximize thermal efficiency
4) Choose the proper bath fluid – select a compatible fluid for the temperature range and chiller; change fluids as needed or on a yearly basis (at a maximum interval)
5) Keep it thin – choose a fluid with a low viscosity in the temperature operating range
6) Validate integration – test all external control systems prior to integration into the production process, if applicable; external temperature probes, computer control system, etc.

More demanding applications requiring low temperatures <-20 °C can be addressed in two ways. Well-known and stable processes can be cooled by chillers that have a large internal bath volume (>40 l). The large reservoir serves as a cold ballast reservoir resisting any temperature fluctuations but hinders fast temperature changes. Exposure to atmospheric conditions must be avoided when used <-20 °C. At low temperatures humidity can accumulate in the open bath and form ice crystals. This will degrade the recirculator performance and can shorten the bath fluid lifetime. A second approach utilizes highly dynamic temperature control systems which supply a broad temperature range (-91 to +250 °C) using a small internal fluid volume. The bath fluid never contacts atmospheric conditions thus eliminating the possibility of ice formation. The combination of a small internal bath volume, strong cooling capacity and a powerful pump enable quick responses to external events (exotherms) and fast pre-programmed temperature profiles.

Chillers can also be integrated with a computer for remote programming and data capture. Communication from the chiller via a built-in RS232 port facilitates hard-wired or wireless computer control. The controlling software supports chiller temperature profile programming, data capture of internal/external temperature, cooling power and interfacing to external data-loggers. Use of the software increases peace of mind, frees operators from performing manual data-logging, reduces foot-traffic in the production area and provides a definitive performance log. In large production areas up to 24 chillers can be controlled and monitored from one PC.
Another option supports communication between the chiller and a handheld wireless remote control. This remote control communicates with up to eight chillers monitoring actual and set temperatures and displays the start/stop and alarm status. This frees operators from constantly walking up to the chiller to monitor settings and allows for adjustment of the set point and start/stop of the chiller while ‘on-the-go’.

Scenario: A production process incorporates a chiller as a critical component. This line fabricates product worth >€ 20.000/day. What would you do if the chiller goes down? How much will the down-time cost?
In the overall scheme of capital expenditures the integration of a recirculating chiller into a corporate-critical production process might be financially insignificant (<€ 7.000). The insignificance of this cost is quickly forgotten if the recirculating chiller breaks down and the entire production process ceases. The necessity of a maintenance contract and service for the recirculator is vital. Contingencies such as a spare cooling unit and/or a comprehensive planned maintenance /service contract from the manufacturer can quickly realize their value.

Ignoring the environmental impact of wasting fresh water in processes is no longer a responsible corporate option. A process chiller supplies consistent cooling performance while saving precious tap water and promotes the significance of global natural resource conservation.

Chillers are key components in process operations. Remember to treat them as such and with proper use and maintenance they will provide reliable cooling and cost-savings for many years.

For further information please visit www.julabo.de


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