In many industrial processes, wastewater is a major economic and environmental concern. The cost of collecting, treating, transporting and disposing of plant wastewater is a major contributor to bottom-line manufacturing costs.
Thermal treatment presents a way to control the evaporation of the wastewater, collect any residual, non-hazardous particulate, and treat the resident volatile organic compounds (VOCs) and hazardous air pollutants (HAPs) in a single piece of equipment. Certainly, particular airstreams containing only pollutants with relatively high Henry’s Law coefficients can be economically stripped out with an air stripper. However, a typical wastewater stream contain many other components, and these contaminants do not have a relatively high vapor pressure or a low aqueous solubility.
Combined Air and Wastewater Thermal Oxidizers
While this article has primarily focused on wastewater treatment, some facilities use a thermal oxidizer for both air emission and wastewater treatment. Multi-use equipment can treat the air emissions and facility wastewater concurrently. Existing equipment can be retrofitted to incorporate a wastewater treatment package although such upgrades may change the throughput conditions of an air-emitting pollution control device.
Materials of Construction. The presence of halogenated compounds can create the need for higher-grade materials of construction. Consideration may have to be made should some of the acid byproducts need post-oxidation treatment.
Heat Recovery. With the additional energy required for water evaporation, heat recovery methods often are incorporated to reduce operating expenses.
Equipment Plugging. Heat recovery equipment may be susceptible to particulate buildup, but this can be mitigated by careful consideration of the wastewater composition being treated.
Design Life. Specific applications range from temporary or short-term treatment to permanent installations. Economic consideration to balance the design life, capital expense, operating expenditures and return on investment should be taken into account when developing a solution.
The process of thermal oxidation is quite simple: the untreated process stream temperature is raised to a point where the chemical bonds that hold the volatile organic molecules together are broken. The VOCs/HAPs in the process exhaust stream are converted to carbon dioxide (CO2), water and thermal energy by the high temperature of the combustion process.
When using thermal oxidation for wastewater treatment, the high operating temperatures immediately evaporate the water, leaving the untreated organics exposed to the combustion process. The proper combination of time, temperature and turbulence inside the thermal oxidizer treats the remaining hazardous waste gases before the thermally treated airsteam is exhausted to atmosphere. Resident particulate in the wastewater drops out and can be collected and disposed of during scheduled internal equipment inspections.
In addition to the economic gains that can result from properly applying thermal treatment to wastewater, environmental impacts can leave a positive influence on the surroundings. Many times, the thermal oxidation equipment has a smaller footprint than other mechanical or chemical treatment technologies, which often use a series of equipment packages. If post-oxidation treatment is not required, thermal oxidizer technology is a zero-discharge system, meaning no additional streams — air or water — are required to be treated.
In addition, an environmentally beneficial discharge byproduct may include non-potable water. By condensing the clean exhaust gas, waste heat may be recovered and a significant amount of the thermally treated water can be put to use as boiler feedwater or for irrigation.
Benefits for Industrial Processes
What types of production and manufacturing facilities could use thermal treatment for wastewater disposal? While many facilities can benefit, two examples are chemical filling stations and oil and gas fracking operations.
Chemical Filling Stations. Chemical filling stations deliver products to manufacturing facilities all over the world. As the drums are filled with various recipes, they must be washed prior to reuse so residues do not contaminate a new recipe. The rinse collected from the drum cleaning contains many types of organic compounds. This newly generated wastewater must be disposed of properly.
Several options are possible when selecting the right wastewater destruction equipment for drum filling and tank ventilation. To make the right choice, destruction efficiency, hours of operation and types of chemicals, VOCs or HAPs present should be considered.
Midstream Oil and Gas Fracking. When hydrocarbon resources are trapped tightly in shale formations, releasing them and bringing them to the surface for economical production is a challenge. The average depth of the wells is 7,000 to 8,000 feet below the surface. During drilling, the initial part of the well is drilled vertically; then, the well drill turns and travels horizontally. This horizontal section may span 1,000 to 6,000 feet, and it is perforated to create a series of small holes for fluid and particles to flow through. To open the formation and allow the hydrocarbons to flow, a water solution is pumped in at an extremely high pressure.
At high pressures, the rock fractures, hence the name hydraulic fracturing, or “fracking.” Additives and sand in the water mixture hold open these fissures, allowing recovery of the hydrocarbons. They are brought to the surface with the water used for fracking.
Much of this water has to be treated because it cannot be reused for further fracking. On-site treatment of the wastewater is one of the methods many are considering in lieu of hauling it away for off-site treatment or disposal.
In conclusion, separation and treatment of VOCs and HAPs using thermal oxidation can be an economically and environmentally responsible solution for manufacturers and processors. For some applications, a hybrid thermal oxidizer, which is designed to handle process airstreams and wastewater, may prove the best choice. Selection of the right thermal oxidizer technology makes a difference when evaluating thermal treatment technology as a viable alternative for managing wastewater treatment. A careful balance of process requirements, design life, capital expenditures, operational expenditures and return on investment is key to determining the optimal solution.