Heightened awareness surrounding environmental protection has highlighted wastewater treatment as a pressing issue. Cities and municipalities are trending towards tough requirements on the quality of effluent being discharged into water streams. As a response, wastewater treatment processes have been improved in terms of efficiency and footprint in recent years. This article looks into a modern wastewater treatment process and how immersion heaters are playing an important role in making it more efficient and economical.
Wastewater is usually produced as a byproduct of an industrial process, commercial activity, or domestic household process. Wastewater treatment is mandatory before discharging fluid into the sewage stream. This ensures that health and safety regulations are met.
Usually, pre-treatment wastewater is laden with heavy metals and carcinogenic compounds which are detrimental to human health and wildlife. Another important aspect is that increasing environmental protection regulations have mandated that these treatment processes are mandatory to prevent heavy fines and potential legal actions if they are released untreated or even partially treated.
The wastewater treatment process can be broadly divided into 8 stages:
If the stream requires further processing for the conversion to potable drinking water, it goes through the process of distillation. Distillation or evaporation is a unique separation process that removes water from the pollutants by changing the physical state of the water from liquid to vapor.
Distillation plays a crucial role in the conversion of effluent water from the wastewater treatment process to potable water. Traditionally atmospheric evaporation was used where heat either through a combustion method or steam was used to heat the influent water to change the physical stage of the water. Although simple and widely used, this is an energy-intensive method requiring a significant investment in the infrastructure (Boilers, pumps, evaporators, etc). It is also maintenance intensive.
An important advancement in water purification technology is Mechanical Vapor Recompression (MVR). MVR can provide advantages of a compact more efficient system at a fraction of the cost of traditional distillation processes.
In MVR, rather than using a thermal fluid-like steam, the water in the primary evaporator or heat exchange is heated using an immersion heater. For example, a flanged heater can be inserted into multiple areas around the primary evaporator. The water vapors are taken out of the system and are compressed by a positive displacement compressor.
The process is adiabatic, meaning that it does not involve the transfer of heat and mass between the boundaries of the compression chamber. The vapors are at higher temperature and pressure compared to the inlet of the positive displacement compressor are passed through a heat exchanger to heat up the water in the primary heat exchanger. The vapors convert to distillate which is either used up for making up the distilled water or passed through a secondary heat exchanger where the incoming water into the primary heat exchanger is preheated. This is a much less energy-intensive process compared to the atmospheric evaporation process and is more efficient.
One of the critical applications of the immersion heaters not limited to the wastewater treatment is in industrial process winterization. When one talks about of winterization of the process, the heat tracing comes into mind immediately. However, process heating and heat trace are remarkably different methods.
Heat trace keeps the process heat in the system while an immersion heater regulates the temperature and provides heat to reduce any condensation in the piping. Immersion heaters provide a step improvement compared to other methods of the process heating like steam or combustion-based systems which have severe performance limitations when it comes to subzero temperatures. The improved performance of the electric immersion heaters due to their ability to maintain precise temperature compared to steam-based systems and fast response due to load variation makes them a favorable choice of process heating in mid to large size industrial process winterization.
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