Refineries store feedstock, process and waste materials in tanks and other storage containers. Sludge accumulates in the bottom of the tanks due to suspended solids dropping out and gathering over time. Therefore, the tanks require regular cleaning to ensure optimal efficiency and effectiveness.
The basic steps of tank management involve mobilizing sludge to prepare a "slurry" to be removed, cleaning the tank, and then managing the waste that's removed. When making decisions regarding tank cleaning, refineries weigh several considerations including tank down time, environmental and safety risks, and what to do with residues.
Due in part to stricter regulations and new technologies, refinery operators are increasingly looking to service providers to clean tanks while minimizing environmental impacts. Being safer and "greener" doesn't have to mean extra costs when reductions in injuries and disposal costs (plus the value of product recovered) are taken into account. In Ontario, for example, new Land Disposal Restrictions (LDR) now prevent hydrocarbon-contaminated sludge from being sent directly to land farms or landfills.
Conventional disposal-oriented tank management involves removing sludge and sending it to a haz-waste landfill or incinerator. The tank is taken offline and sludge in the bottom is diluted via the adding of light hydrocarbon-based fluids (to mobilize the solids). Once removed, the liquid slurry requires solidification in order to be suitable for disposal.
Each of these steps significantly increases the volume of material requiring disposal, plus adds safety risks from confined space entry into the tank, greenhouse gas (GHG) emissions (from transporting large volumes), and opportunity costs (from taking the tank offline).
Newalta's approach
Alternatively, in keeping with its "What if Waste Wasn't?" operating philosophy, Newalta looks at tank cleaning as an opportunity to recover value from what has traditionally been considered refinery waste, while reducing environmental impacts. The company's approach reduces the volume of waste sent for disposal by up to 95 percent and maximizes hydrocarbon and water recovery.
From the initial consultation and project scoping to cleaning the tank and managing the waste, Newalta tailors tank management solutions to the specific needs of the customer. The company has experience minimizing oil and gas industry waste, and recovering 1.5 million barrels of crude oil each year.
For refineries, safety is of the highest priority. Risks associated with tank cleaning include having extra people onsite and exposure to dangerous substances such as H2S and benzene. In Ontario, Newalta's Onsite group (based in Sarnia) maintains a Total Recordable Injury Rating - a number measuring the frequency of on-the-job injuries - of zero. The onsite safety program includes core and site-specific training, daily safety meetings, self-contained installations to prevent leaks, and odour and vapour control systems.
The company's typical Newalta tank management process includes:
• Consultation, imaging and sampling: Newalta works with the customer to determine the scope of the project and set expectations. Sludge is profiled using infrared technology and 3D-modeling to analyze tank contents and determine optimal processing methods.
• Non-entry tank decontamination and sludge suspension: Robotic or automated technology reduces the need for confined space entry. Tank materials are liquefied to mobilize and suspend solids in the sludge, which is then removed to maximize product recovery potential.
• Centrifugation, filtration and product recovery: Centrifuges separate solids from liquid components in sludge. The company's centrifuges are specifically engineered to manage oily sludge found in tanks. Depending on the sludge profile and contaminants in the tank, a decanter centrifuge is used to separate solids and hydrocarbons, or a tri-canter to separate oil, water and solids. In the case of sludge with low levels of solids, a filtration system can be used.
• Disposal: By recovering oil and water from sludge, the amount of solids requiring disposal is reduced by 85 to 95 percent. The remaining solids are sent off-site for safe disposal.
• Tank cleaning and coordination of inspection and maintenance: After sludge is removed, tanks are cleaned using safety-oriented tank entry protocols. If required, inspection and maintenance are coordinated with appropriate third parties.
Eliminating disposal, recovering brine
While Newalta's approach already reduces tank waste by up to 95 percent, the company is exploring opportunities to recover the inherent energy value in the minimized solids, thus eliminating the need for disposal altogether. This includes testing of innovative processes and technologies to treat the waste such that it can be used as an alternative fuel (in cement kilns, for example).
In addition to tank management, Newalta partners with refineries to manage and recover brine from salt cavern operations. Salt caverns are used to temporarily store hydrocarbons and liquefied petrochemicals. Brine (water with very high salt concentrations) is created when the caverns are first developed, and is used to displace the hydrocarbons from the cavern as well as maintain the storage volume and integrity of the cavern while not in use.
Brine is stored above-ground in open reservoirs, where it's exposed to rain and runoff water. Excess brine water must be managed, and with its extreme salinity, isn't suitable for traditional water treatment and discharge. Therefore alternative methods of disposal must be used.
Rather than simply discarding brine water as a waste, Newalta introduced evaporation technology as a more environmentally progressive alternative. The excess water is evaporated and brine is re-concentrated and returned to customers. To make this highly energy intensive operation more cost effective, the company uses excess steam produced by the customer's boiler facilities to power the evaporation process, thus transforming another waste material into a resource.
In the future, Newalta intends to partner with refineries to develop long-term design, build and operate (DBO) tank management facilities on their sites. This will allow for continuous, cost-effective removal and recovery of hydrocarbons and water from minimal amounts of tank sludge, thus eliminating the need for major tank cleaning projects altogether. HMM
Pat Carswell is Senior Operations Manager, Onsite Services, Eastern Canada in Burlington, Ontario. Contact Pat at pcarswell@newalta.com Mark Conway is District Manager, Onsite Services, Western Canada in Calgary, Alberta Contact Mark at mconway@newalta.com