Some grades of emulsion require heating during storage and use. Table III-1 from AEMA’s A Basic Asphalt Emulsion Manual may be helpful. The end user should check with the local AEMA emulsion supplier for their suggestions on storage temperatures.
Several types of heaters may be used for asphalt emulsion. The main requirement is that the heater be regulated to provide the desired temperatures and that it use indirect heat instead of direct heat, such as an open flame.
These self-contained heaters heat a special heat transfer fluid using gas or diesel burners or electricity. The heater pump circulates the hot oil through the system and emulsion tank coils (described later). The hot oil temperature must be kept 85° C (185° F) or below as required. Thermostatic controls can be used to set tank temperatures as required.
If the hot oil is used to heat other materials, (e.g., asphalt cement), that require higher temperatures, modifications must be made to the system. The hotter oil can first heat a tank of water and then the water can be circulated through the storage tanks or a special system can use a second recirculating pump and a thermostatically controlled mixing valve to keep the temperature of the oil for the emulsion at the desired level.
Low pressure steam can be circulated through coils similar to the hot oil. This probably is the desired system where steam is already available. A method for moving the emulsion over the surface of the steam coils should be considered. A side entry tank mixer is preferred, but re-circulation by a pump may also be used. Note: Avoid over-pumping/shearing of emulsions.
Water can be heated by hot oil, steam or electricity, and circulated through tanks in the same manner as hot oil and steam. This is a safe method since water seldom gets hot enough to damage the emulsion.
In recent years solar heaters have been used to heat hot oil or water which in turn heats the emulsion tanks.
Electrical heaters are available to heat the emulsion. These heaters offer the advantage of eliminating tank coils and related plumbing required for hot oil, steam or water. Each tank heater is separately controlled, thus making it simple to set tank temperatures at different levels or individually cut off the heat to any tank. Again, some method for moving the emulsion over the heating surface should be considered. This will prevent the emulsion from localized over-heating and contribute to more even product temperatures.
Heating coils are placed in tanks as previously noted for circulation of hot oil, steam or water. Either thick wall or standard pipe or tubing is used. Finned tubing is not recommended for emulsion tank service. As an emulsion tank drains, emulsion gathers in the voids between the fins. As soon as the tank is empty, the emulsion will begin to break and coat the fins. Over time, the fins will become plugged and will not transfer heat very well. The only choice is to clean the coils by hand (difficult and time consuming), or use a solvent. This raises issues of cost, waste disposal, and product quality. The hot oil system uses black pipe or tubing.
The amount of coil required for each tank depends on size of tank, amount of tank insulation, wind velocity, lowest expected ambient air temperature, amount and type of insulation, type of emulsion, and how rapidly the emulsion temperature must be increased, if at all. Consult a heating specialist for information on this.
Emulsion lines and transfer pumps must be heated, especially if emulsion is used during winter. This insures uniform emulsion temperature and trouble free pump starting. Lines and pumps must be heat jacketed or traced and then insulated.