Proper selection ensures a safe thermal fluid system that will provide peak performance for many years.
A well-designed thermal fluid heating system can provide consistent, reliable and safe operation for decades. By selecting the right system with properly sized equipment, it can run at peak performance for its owner, optimizing output and production for a specific process. A properly designed thermal fluid heating system is composed of the following four main components plus at least one user:
- A thermal fluid heater.
- Circulating pump(s).
- Expansion tank.
- Catch tank.
Depending on the level of system complexity, one could also use additional system controls, control valves, secondary loops, heat exchangers or countless other system variations. But every system should include — at a minimum — the core pieces of equipment listed above. Here are a few tips to use as a baseline to help size and select each of these core pieces of equipment in a basic thermal fluid system.
Sizing the Thermal Fluid Heater
The heater needs to be sized for the maximum BTU/hr requirements of the system during peak load. If the customer plans on expanding in the future, the future BTU/hr requirements also should be considered. In most cases, the customer knows what size heater is required. Otherwise, the heat required must be calculated by using the following equation:
Q = M x CP x ΔT
Q is the heat required.
M is the quantity of material being heated.
CP is the specific heat of material
ΔT is the difference between final temperature and initial temperature.
This calculation must include the product being heated as well as the vessel containing the product and any piping that carries the hot fluid to the product. Remember that the vessel must heat up in order to heat its contents. Heat losses also must be taken into consideration, and proper engineering practices must be followed to determine an appropriate safety factor.
Determining the Required Flow Rate
In many cases, the standard flow rate of the heater can be used as the system flow rate. This is always the simplest approach. For heaters with a fixed flow rate requirement, having a system flow rate requirement that is different than the heater flow rate presents some additional design challenges. In these situations, if the user requires a higher flow rate than can be passed through the heater, a heater bypass is required to carry additional flow around the heater. If the user requires less flow than is required for the heater, the heater must still see the required flow rate, so then a system bypass may be required to manage the additional flow around the user. Alternatively, a three-way control valve may be considered to divert the additional flow around the user.
When flow rates have to be calculated, it is important to revert back to the equation to determine how much flow is required to remove the appropriate amount of heat from the thermal fluid flow stream. However, for this calculation, we must rearrange the equation to solve for flow rate. It looks like this:
M = Q / (CP x ΔT)
Q is the heat being transferred to the user from the thermal fluid.
M is the required flow rate of the thermal fluid
CP is the specific heat of the thermal fluid
ΔT is allowable temperature drop for the thermal fluid across the inlet and outlet of the user.
Read more about sizing here.