Winterizing with electric process heaters saves money and maintenance headaches

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By Richard Hartfelder

PlantServices.com

Keywords: winterizing

Proper winterizing efforts require a broad, more thoughtful approach. Of the many options available, the use of electric process heaters, although not exceptionally well known or understood, is often the most practical and effective approach to winterizing.

As winter approaches, processing plants and engineering firms begin to turn their thoughts toward preparing for the extreme weather conditions they will soon be facing.  Typically, when individuals working in the processing industries think of “weatherizing” their plants, they conjure up images of “heat tracing.”  However, proper winterizing efforts require a broader, more thoughtful approach.  Of the many options available, the use of electric process heaters, although not exceptionally well known or understood, is often the most practical and effective approach to winterizing. 

Most processing industries have multiple applications where winterization should be made a significant priority – to avoid maintenance headaches or simply to improve processes.  Below are just a few examples, by industry, of applications where process heating is recommended and can have a substantial positive impact.

Process Heating

Large processing plants, such as refineries, electric power plants and pulp and paper mills, primarily use either steam or fired types of heat sources (gas, coal or oil) for large bulk heating and processing requirements.  However, there are many instances where electric heating should be employed to overcome the limitations of these systems (especially steam) during periods of exceptionally cold weather.  Two good options are electric steam superheaters and trim heating systems.  In both cases, these systems consist of in-line (circulation) heaters coupled with temperature control systems.  Steam superheaters prevent steam from reaching its saturation point within long, remote pipe runs by boosting the steam temperature well into the superheated region.  This same in-line concept is used for electric “trim” heaters.  These heaters are used in conjunction with steam systems to provide steam at the process point with the correct temperature and pressure.  An electric heater and control system respond much faster to load variations and can be controlled much more accurately. 

At a minimum, when steam heat loads reach plant capacity, an electric heater system should be considered as an alternative economical solution, versus expanding the facility’s boiler capacity or adding an entire new boiler system.

Calendar rolls, used within pulp and papers mills, are a good example of an application where electric process heating is an ideal solution.  Calendar rolls are located at the ends of paper machines and are used to increase paper smoothness, improve final surface finish and act as a final thickness gauge.  Fluctuations in temperature naturally cause the roll to expand or contract, and therefore greatly impact the quality of the finished product.  To avoid fluctuations (which can be significant in winter months), many paper mills use either electrically heated hot oil heat transfer systems or forced ducted air systems using tubular or finned heating elements.  These types of electrically heated systems, mated with the proper control systems, can achieve temperature uniformity within 1°C or better. 

Operating Temperature Maintenance

As the thermometer plummets, oils become increasingly viscous, especially fuel oils, making pumping difficult.  In addition, as temperatures fall below -0°C, oils such as diesel #2 have the added problem of paraffin wax precipitating out of the oil solution, causing wax build up and deposits and potentially clogging fuel nozzles on boilers, engines and other equipment.  Watlow’s solution to this problem was to develop an ‘O’ shaped over-the-side heater.  These electric heater assemblies employ robust, rigid tubular heater elements in an ‘O’ shape attached to an unheated riser mounted to a flange plate.  Either a local or a remote control box can be used with the heaters.  The system uses a low wattage surface loading to warm the oil, yet not to the point of element coking and/or oil degradation.  Additional precautions include a high limit temperature sensor attached to the heater element “bundle,” and a high limit control circuit set to trip well below the fuel’s flash point.  Overall, the use of electric heaters within tanks is a simple solution to ensure that fuel oil is ready to flow for main system use, or that back up fuel tanks, used by standby generator systems, are ready at a moment’s notice.

Another place where cold can wreak havoc is on tank farms.  Crude tank farms typically employ some type of temperature maintenance system – either steam loops or some form of internal electric heating.  Yet, there are some lesser-known electric heating designs that often offer substantial energy savings over these methods.  For example, one economical alternative to steam loops is the use of pipe insert (or bayonet type) electric heaters.  These heaters can be removed and serviced without having to drain a tank’s contents.  Watlow typically recommends installing additional tubular elements in the heater design to function as spares should any of the elements fail.  This significantly reduces downtime by allowing maintenance to simply rewire to the spare tubular heaters, without having to remove or replace the heater bundle. 

Pipe insert heaters are essentially composed of pipe vessels mounted through the sides of storage tank walls.  Screw plug or flanged immersion heaters are then inserted into these bayonet-like wells.  The wells may remain dry or may be filled with a heat transfer fluid to improve heat transfer to a tank’s contents.  The exact design selected depends on the type of oil, desired temperatures, tank capacity and other variables.  These heaters normally need to be AMSE code stamped and/or obtain a CRN to ensure proper operation in hazardous locations.