In many pilot-plant or production facilities, temperature control systems are like the wallflower at the junior high school dance -- they are not the most technical, expensive or exciting equipment in the room, and they 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. In many ways, “wallflower” is an appropriate appellation for a chiller: though it may operate in relative obscurity in the process, it is an essential part of the whole whose reliable performance is extremely important.
Scaled-up pilot or production processes introduce new challenges for temperature control systems. The thermodynamic profile of the process must be thoroughly understood, and the chiller must be specified with sufficient cooling capacity to reach the desired process conditions. Typically, processes incorporate a capacity safety factor of approximately 20 to 30 percent.
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 (greater than 5 gal [22 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.
In addition, the cost of the water supply/sewer charges weighs significantly in operating budgets. For example, a moderate flow of 16 gal/min for a working year in the New York City and San Diego areas costs more than $17,000/year (assuming $6.76 and $6.97/hcf). Also, fresh water is a limited resource with periodic rationing in various locations. If water restrictions activate in your plant area, what do you do? Moreover, 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 (greater than 5 ton or 20 kW) can control dedicated cooling processes such as condensers, packaging systems, reaction vessels and semiconductor applications. Circulators with a large pumping capacity (20 gal/min and 85 psi) can even control multiple systems while meeting the cooling requirements.
Depending on the process, circulators accommodate the use of a range of fluids for temperature control, including water, glycols, alcohols and silicones. 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 of less than ±1°C deliver peace of mind that the process temperature conditions remain constant and reproducible.
Are You Getting the Most From Your Chiller?The proper installation, proximity and connection of the recirculating chiller to the application is paramount in effecting 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:
- Minimize tubing length. Keep the tubing as short as possible and well secured.
- Maximize thermal exchange. Utilize tubing and connectors with the proper diameter. Avoid bath fluid flow path restrictions.
- Insulate. Install insulation on all tubing, connections and vessels to maximize thermal efficiency.
- 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).
- Keep it thin. Choose a fluid with a low viscosity in the temperature operating range.
- Validate integration. Test all external control systems prior to integration into the production process and, if applicable, external temperature probes, computer control system, etc.
A second approach utilizes highly dynamic temperature control systems that supply a broad temperature range -- for instance, -183 to 482°F (-91 to 250°C) -- using a small internal fluid volume (5.5 gal). The bath fluid never contacts atmospheric conditions; thus, the possibility of ice formation is eliminated. The combination of a small internal bath volume, strong cooling capacity and a powerful pump enables quick responses to external events (exotherms) and fast preprogrammed temperature profiles.
Can We Communicate?Chillers also can 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 dataloggers. Use of the software increases peace of mind, frees operators from performing manual datalogging, 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 setpoint and start/stop of the chiller while “on-the-go.”
In conclusion, get to know your wallflower. 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 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.