Numerous types of heat exchangers cover a broad range of applications, and specialty heat exchangers are often found in many kinds of industrial applications, such as downstream refineries. When a heat exchanger is used to cool a representative sample within processes for accurate analysis, it is commonly referred to as a sample cooler.
How Heat Exchangers and Sample coolers work
A sample cooler removes excess heat from the sample to a point that’s safe for the instrumentation and operators. It’s simply a small shell and coil heat exchanger that works like this:
- The sample to be cooled flows through the tube side of the cooler.
- The cooling fluid, usually water, flows through the shell side of the cooler.
- The cooled sample is taken to a laboratory for analysis or piped to on-line process instrumentation for continuous monitoring of certain properties such as conductivity, pH or chemical constituents.
The most common types of heat exchangers include:
- Single helical tube or coil
- Spiral tube or coil
- Dual tube coil (DTC) or tube-in-tube
- Shell and tube
- Plate heat exchanger
For safety and efficiency, it’s critical to choose the right heat exchanger for the right application. Selecting a one-size-fits-all heat exchanger for a process may seem to be less expensive at first, but can end up being inefficient, uneconomical and hazardous to operators, equipment and assets.
Heat exchanger choice depends on:
- Amount of heat to be exchanged
- The specific type and thermo-physical properties of both the process and cooling fluids
- The temperature of the fluid
- Liquid or gas phases, and whether a phase change is required
- Process pressure and flow rate
- Characteristics of the cooling water, such as chlorides, calcium or hardness, or high total dissolved solids
- Efficiency relative to size
- Physical space within the process for the heat exchanger
Key considerations for refinery sample cooler installation
- Choose sample coolers designed for various flows and pressures. This includes considering cooler sizing and construction of materials. The recommended construction materials are stainless steel or an alloy when chlorides are present, as chlorides will quickly eat through stainless steel.
- Water supply/return orientation – Water supply/return orientation is dependent on size and construction specs of the sample cooler. Sample coolers can be mounted either vertically or horizontally, but it’s best to mount them vertically on high-temperature lines. Coolers are also typically installed with isolation valves in the cooling water piping to facilitate service.
- Proper configuration should include:
- Process throttle valve
- Cooling water flush
- Adequate cooling water flow
- Routine maintenance plan of coils and shell
- Verification of proper tie-ins
- Maintain flow rates with needle valves. All cooling applications need a needle valve to maintain flow rate within the parameters of the coolers capability.
- Provide flush capability. Employ a ball valve to flush any unnecessary materials, such as mud, particulates and calcium build up, from the cooler.
- Conduct regular maintenance and upgrades. After installation, it’s important to identify when maintenance/upgrades will be needed. Most coolers need only occasional descaling of the shell side, which can be done chemically or mechanically after removing the shell. The cooler should be warm at the top and cool at bottom, as measured by an infrared thermometer. If the heat moves down the cooler, repairs are needed.