T. Eggert, Veolia Water Technologies & Solutions, Portland, Oregon; and D. HARBS, Veolia Water Technologies & Solutions, Costa Mesa, California
Water reuse within a particular industrial facility is not a new idea. Power industry facilities operating in arid areas have been designed to be “zero liquid discharge” (ZLD) for more than 20 yr. So, why hasn’t water reuse been more widely applied to the hydrocarbon processing industry (HPI)?
Complex industrial facilities like refineries or chemical plants are large consumers of water. Some plants can require more water in their cooling towers, steam generators and process applications than the volume of crude oil they process. In the past, the water sources for these facilities have been abundant and procured at a very low price. Wastewater discharge was also easily handled and inexpensive. In addition, some of the contaminants found in HPI and chemical processing industry (CPI) discharge can be problematic to remove or treat, making the design and operation of a water reuse system much more complicated and expensive then what might be found at a typical ZLD power facility. Therefore, the incentive for water reuse has been low for HPI/CPI industrial complexes.
Nevertheless, water reuse within refineries and chemical plants is likely going to become a reality for many facilities—the availability of water supplies to industrial complexes becomes less certain year after year, as wastewater discharge is coming under increased scrutiny and regulations (FIG. 1). Sustainability is a common discussion topic throughout all aspects of industry, and adopting more sustainable operation practices is not only imperative, but can provide positive economic return through:
One mean to address this reality is the reuse of plant wastewater to replace influent water supplies.
Qualifying a water reuse project begins with evaluating the inputs and the outputs of the process. Any reuse project must be evaluated on multiple levels: logistics, cost savings and feasibility are primary considerations, while water quality of the source water and final product use can determine the overall viability of the project.
Inputs. Reuse projects identify incoming freshwater streams (e.g., municipal potable feed, well water, clarified river water) for reduction and replacement. The reduction of the flow of the incoming streams through water conservation techniques such as leak repairs and operational optimization of the end users (i.e., cooling towers, boilers, desalters) is the first step in any water reuse project. The plant can then evaluate the potential use of current wastewater streams to directly replace these incoming streams and qualify the treatment processes required to bring this wastewater back to the front end of the plant.
The source water for a waste recycle project will typically be the treated wastewater effluent from the facility. In the HPI and CPI, the wastewater can frequently be segregated between the process water and non-process contact water. In this case, the final use of the recycled stream may determine which of these streams is most applicable for treatment and recycle. An example of the process and non-process wastewater from a hydrocarbon processing plant can be seen in TABLE 1.
Some of the constituents found in these waste streams that can be problematic for the treatment process and for reused water users are: aluminum, chlorides, hardness, manganese, phosphate, silica, other heavy metals that might come in with the crude slate, and processing byproducts such as hydrogen sulfide, ammonia and hydrocarbon organics. Due to this wide range of potential “bad actors,” it is imperative that each source water for the reuse project be thoroughly analyzed for all of its concentrations of all parameters, and their variability understood.
Outputs. The output or product water from a reuse treatment project can be defined by the targeted end user of the water stream. Large water users in an industrial facility, such as cooling towers and steam system make-up, should be considered a priority due to their high intake and relative risk associated to chemical imbalance and contamination (FIG. 2). The water quality standards of these streams must be met before a new make-up source can be introduced.
Cooling tower make-up may require as much as 99% removal of the organics in a reuse water stream to prevent the proliferation of microbiological activity that can lead to biofouling and other issues. These can include contaminants such as ammonia, chemical oxygen demand (COD), phenols, oil and gas, and other forms of dissolved organics. This can require extensive treatment through processes like filtration, membrane separation, and biological and chemical oxidation.
Steam generation will have even higher water purity requirements with the organic material being treated for removal, as well as some level of dissolved solids removal. Low-pressure steam generation will require at least hardness removal through zeolite softening, while medium-pressure and high-pressure steam systems will require anything from membrane purification to full demineralization before being usable as boiler feedwater.
Reuse project options. The source wastewaters and the ultimate use of the treated wastewater will be the deciding factor as to which stream is the best option for further treatment and recycle. The non-process contact water is typically higher in inorganic salts like calcium, potassium, magnesium, chloride and silica. This makes it harder to treat for use in a steam cycle system, but it may be a better candidate for additional treatment to be used as cooling tower make-up. The process contact-treated wastewater is often high in sulfur and nitrate, which would be detrimental to treatment for use as cooling tower make-up. Proper treatment for removal of these organics could potentially make this stream a good candidate for use in boiler feedwater pretreatment systems.
The final use of the recycled water, and the potential waste product of a treatment process, will be important considerations when choosing a treatment process for water recycle. Technologies like ultra-filtration [(UF) 0.02 µm–0.05µm] or reverse osmosis [(RO) 0.001 µm–0.0001µm] membranes can generate high-purity water with manageable waste stream volumes. The product of these processes can be blended into cooling tower make-up streams to reduce freshwater demand. The high purity of the RO product may meet the criteria for direct use in steam generation or go on to a second purification step such as dealkalization, demineralization or second-stage RO treatment. A membrane bioreactor (MBR) is a treatment step that can be used if the source water contains significant amounts of organics that require removal. Frequently, the MBR process will be followed by additional polishing treatment to meet the water quality standards required for the identified reuse application.
Final plant effluent. Assuming the reuse project is not a full ZLD operation, the amount and quality of the final effluent stream from the reuse treatment facility must be determined. The final effluent stream will be based on the entire facility’s water balance. This final stream can be a combination of recycled process streams as well as solids, precipitated solids and concentrated liquid streams. Disposal of these streams must be accounted for in any water reuse project because, although the effluent flowrate may be decreased, its composition and concentrations will also differ and may require different handling considerations.
Maintenance and operations. When compared to the whole facility’s maintenance program, utility repair planning often does not rate as a high priority. Similarly, operator and engineering support given to the operation of non-profit center units is commonly given a lower priority. However, given the complexity and importance of a water reuse project’s operation to a facility, additional attention to planning must be given to the maintenance and operation of the treatment plant. This can ensure that the whole facility operates reliably and efficiently within the sustainable targets set by the water reuse project.
Water reuse Example #1. Although the HPI and CPI have yet to show a large interest for water reuse, some facilities have implemented such projects successfully. One example is a large refining complex in the Gulf region (U.S.) that was a large consumer of fresh water in an area where the resource was stressed. Embracing the need for conservation and environmental stewardship, the oil refinery committed to a $200-MM wastewater improvement project. To be applicable, the operation required an advanced wastewater treatment facility capable of:
This refinery’s unique wastewater reuse treatment solution would begin with holding tanks where oil, water and oily solids separate by gravity. Oil is skimmed off the top as it floats above water and is reprocessed within the refinery. The sediment and oily sludge sink to the bottom, and the sludge is removed and reprocessed or disposed of safely. The remaining wastewater continues to a dissolved air flotation unit for enhanced oil and water separation. The wastewater then proceeds to biological treatment followed by filtration through ultrafiltration hollow-fiber membranes. This combination process (MBR technology) creates a permeate largely free of organics, ammonia, nitrite, nitrate and other impurities. This treated wastewater meets the quality standards to feed the demineralization plant that makes feedwater for the ultimate end user of the reuse water, the steam generators (FIG. 3).
Water reuse Example #2. Another refinery’s freshwater makeup source was both expensive and of poor quality for the primary cooling tower makeup. The low quality of the water required the system to be operated at low cycles, causing an excessive blowdown rate to a non-process contact wastewater pond, and forcing an equally high demand in makeup water. The idea of reusing the pond water for cooling tower makeup was developed and nano-membrane technology was chosen as the reuse treatment approach. The quality of the nano-treated water was such that cooling tower cycles could be increased by four times, reducing the blowdown rate by 75%. The quality of the nano-treated water was so much better that a new cooling chemical treatment program had to be implemented, focusing on corrosion control now that little risk of deposition existed with a much improved feedwater quality.
Takeaway. Successful water reuse requires the understanding and evaluation of water quality inputs and outputs standards in the initial phase of a water reuse project. This knowledge will improve the project’s viability and chances of success over the long term, making them both environmentally and economically sound. This is important, as these projects will become ever more necessary as the situation around water scarcity worsens and stricter regulations are introduced. HP
TIMOTHY W. EGGERT is Technical Director at Veolia Water Technologies & Solutions. He has more than 43 yr of experience in the water treatment industry as a process engineer and a chemical solutions provider, primarily in the refining and power Industries. Prior to his current role, he was a Senior Technical Consultant at Veolia since 1999 and was been involved with numerous steam boiler, cooling and wastewater projects throughout the U.S. Eggert has been involved in the application of cooling water treatment programs for diverse makeup sources, including municipal reclaim waters, as well as the use of non-phosphate cooling treatment program applications in the refining, power and chemical processing industries since the early 2010s. Eggert earned a BS degree in chemical engineering from the Massachusetts Institute of Technology (MIT).
DAN HARBS is a Senior Technical Consultant at Veolia Water Technologies & Solutions with 26 yr of refining chemical treatment experience. He has treated all aspects of refinery chemical applications, including process side antifoulants, corrosion inhibitors, desalters, fuel additives, cooling towers and steam systems, as well as primary and secondary wastewater treatment. Harbs has co-authored numerous published papers on topics such as reactor bed fouling treatment, the successful treatment of cooling towers using reclaimed water, the development of new cooling tower corrosion inhibitors, and heat exchanger monitoring. He resides in Southern California with his wife and two sons.