Pressure Testing Process Path Prior to Final Assembly
Every cylindrical bore block is pressure tested prior to installation in the steel shell. The process path through the block is fitted with nozzles, baffles and ports to facility the pressure testing. Any leakage of the process path can be quickly identified before the assembly is mounted inside the steel shell. The pressure testing is repeated after final assembly as well.
Pressure testing is typically performed at 100 psi. Customer requirements can be accommodated up to several hundred pounds if necessary.
Pressure testing process path prior to final shell assembly.
PTFE Bushings Protect Graphite Immersion Plate Heaters
Shown here in white PTFE, a bushing is installed in a graphite immersion plate heat exchanger. The bushing provides a number of features that enhance the lifetime of the plate heater. While bushing could be manufactured from a range of materials, PTFE provides an excellent blend of mechanical characteristics and chemical compatibility or corrosion resistance.
PTFE Bushings Protect Graphite Immersion Plate Heaters
Graphite can be threaded with small diameter pipe threads for service connection (to steam lines for instance); however the small threads are relatively weak due to the small amount of graphite surrounding the threads. By using a larger diameter thread and a bushing, the strength of the interface is improved substantially.
The PTFE bushing also has excellent dielectric properties that reduce possible galvanic action at the fitting interface.
The PTFE bushing also reduces damage to the graphite heater if excess mechanical force is placed on the service piping. The service pipe may damage the bushing without breaking the graphite.
Threading service fittings directly into graphite can be an intimidating processes, since damaging the graphite plate heater service port is costly and time consuming to repair. Factory installed bushings greatly reduced the risk of installation related damage.
Active Chemical Systems Inc. encourages the use of PTFE bushings on all direct threaded graphite service connections.
Bore Size and Spacing are Critical to Efficient and Robust Heat Exchangers
Bore Size and Spacing are Critical to Efficient and Robust Heat Exchangers
Unlike other manufacturers, Active Chemical Systems designed blocks with larger bore holes to reduce the likelihood of clogging and extend the service live between rebuilds. However, large bore holes with closer spacing results in a manufacturing challenge. Rather than increase the spacing between bore holes, Active Chemical Systems has developed full automated custom CNC systems to automatically and very accurately bore close-spaced holes up to 72″ deep.
Scaling Buildup on Immersion Heater
The image below shows an immersion plate process heat exchangers with a build-up of chemical scaling from the pickling bath. The scaling reduces the immersion plate exchangers efficiency because the scales are less thermally conductive than the graphites. The build-up can be removed either chemically or mechanically; however, this is time-consuming. Some pickling solutions and processes are more prone to depositing scale on the plate heater.
Reduce Scaling with Teflon Coating
Active Chemical Systems offers optional PTFE coating to reduce the scaling build-up rate. Scaling is less likely to form on the PTFE surface and is easier to remove.
Removing scaling can potentially damage the graphite immersion plate heater. Using a pressure washer with excessive pressures can strip the surface of the graphite. Any time impregnated graphite is stripped from the heater surface, there is a possibility of creating porosity that could lead to leakage of the steam or water into the pickling bath.
Active Chemical Systems, Inc. offers optional PTFE coating to reduce the scaling build-up rate. Scaling is less likely to form on the PTFE surface and is easier to remove.
Graphite Immersion Plate Heat Exchanger Fins
Surface Area and Thermal Conductivity
Graphite’s exceptional thermal conductivity combined with high surface area maximizes plate heater efficiency.
Thermal Conductivity
Graphite’s combination of exceptional corrosion resistance and thermal conductivity makes it an excellent material for heat exchangers. While individual graphite sheets display strong anisotropic thermal characteristics (since phonons propagate quickly along the tightly-bound planes, but are slower to travel from one plane to another), the amorphous graphite material used in heat exchangers “averages out” the anisotropic characteristics so that the thermal conductivity is essentially equal in all directions.
Surface Area
A key feature of an immersion plate heater is its compact size. While graphite is thermally conductive, it still requires a significant surface area to transfer heat efficiently. The surface area could be increased by make the plate heater very thin, and extend is height and width to fill the tank. This would compromise the strength of the immersion heater and eliminate a key feature, it’s compact size.
Fins and Grooves
To increase the surface area while retaining the compact size, fins and grooves are machined into the sides of the plate heater. The dimensions of the machined features are chosen so that the fins are strong and maintain mechanical integrity while increasing the surface area as much as possible. In practice, properly engineered grooves or fins increase the surface area by 100% over a smooth surface.
High-Efficiency Immersion Plate Heaters
It all begins with an idea.
Graphite Immersion Plate Heaters - more accurately called graphite immersion plate heat exchangers, are ideal for control pickling tank temperatures. Among the benefits in pickling tank application are corrosion resistance, durability, efficiency, and reparability.
Corrosion Resistance - Graphite Immersion Plate Heaters are typically sold with Impreg-Tite™ graphite to reduce porosity and improve chemical compatibility. The Impreg-Tite™ process includes the use of an industrial vacuum autoclave to ensure deep even penetration of the phenolic resin into the graphite matrix. The resulting Impreg-Tite™ material is impervious to a wide range of chemistry.
Efficiency - Graphite is an excellent conductor of heat and can be formed to maximize surface area by machining "fins" along the length of the plate. The main benefit of an efficient heater is it's compact size. Smaller heat exchangers displace less material and require less space in the pickling tank.
Durability - Unlike fluoropolymer heat exchangers that are composed of coils of tubing, the graphite immersion plate heat exchanger is unlikely to be harmed in the process tank. Due to the poor thermal conductivity of the fluoropolymer, very long lengths of tubing are required. The longer the coil, the more opportunity for the relatively weak tubing to be pierced in the pickling tank.
Reparability - Impreg-Tite™ Immersion Plate Heater's sturdy construction also provides the basis for repair-ability. Most damage tends to be localized to the base of the unit or the steam connection and can easily be repaired at Active Chemical Systems facility in Ohio.