Over the years, Trans Mountain Pipe Line Co. Ltd. (TMPL), a subsidiary of B.C. Gas, Vancouver, had experienced periodic odor problems at its Westridge marine terminal in Burnaby, BC. These odors were created by the loading of sour crudes and condensates.
After installation of a sulfur-scrubbing unit failed to eliminate the odors completely, the company chose a vapor-combustion system designed by John Zink Co., Tulsa, and entered into a unique turnkey contract with the designer that not only yielded the benefits of a turnkey project, but also provided some means of controlling the projects cost.
Early efforts
TMPL operates the only pipeline system transporting crude oil and petroleum products from Alberta to the western coast of British Columbia. This 1,260-km pipeline was built in 1952 to transport crude oil from Alberta to the West Coast markets.
As customer needs have changed, TMPL has altered its facilities and methods to meet these needs. The result is a diversified pipeline operation in which a wide variety of products transported includes crude oil, condensates, refinery feedstocks, refined products, and methyl tertiary butyl ether (MTBE).
The products are shipped through the pipeline to the Westridge marine terminal in Burnaby, BC, which is also owned and operated by TMPL.
At the terminal, crudes and condensates are loaded onto ocean-going vessels, and jet fuel is sent via another pipeline to the Vancouver International Airport.
The dock facility handles tankers ranging in size from 50,000 to 100,000 dwt. Because the terminal primarily loads low vapor pressure crudes and condensates into ships, vapor control is not required by regulation.
The company has experienced odors, however, created by the loading of sour crudes and condensates that have prompted complaints from neighboring communities.
Although the odors were expected to have no permanent effect on the environment, they were a nuisance to the community. Thus, in the early 1990s TMPL began looking for a solution to the problem.
To help reduce the odor problem, TMPL initially installed a sulfur-scrubbing system. This system consisted of two large adsorption vessels containing a medium that would adsorb H2S from the vapors.
The medium did not absorb mercaptans, however, and the system's efficiency varied with such factors as the moisture in the vapors, vapor temperature, and inlet composition.
In a marine loading operation, these parameters change from one load to the next as well as during a single load. This technology was not capable of completely eliminating the odors under these conditions.
In early spring 1998, TMPL contacted John Zink Co. LLC, Tulsa, to inquire about a vapor-combustion system for the application. The advantages of such a system included:
- High destruction efficiencies are achieved. Performance is not sensitive to varying parameters.
- The system is capable of handling a wide variety of products simultaneously.
- The capital cost of the system relative to other alternatives is low.
For John Zink, the more challenging portion of the system design was the sulfur-bearing compounds and the special consideration that was required in burning these compounds.
TMPL chose a unique approach to the project that yielded the benefits of a turnkey project while at the same time maintained control of the project cost.
Design of a marine vapor combustion system (MVCS) for this application required several factors to be considered:
- Safety equipment to protect vessel and personnel.
- Combustion system design.
- Effect of flue gas products on surrounding areas.
Safety concerns
In 1990, the US Coast Guard promulgated regulations for marine vapor-control safety equipment. But the Coast Guard has no jurisdiction over this Canadian terminal, and therefore there was no requirement to follow the regulations.
Nevertheless, because the regulations were developed by an industry committee knowledgable in vapor control and because the regulation is recognized as a safety standard around the world, TMPL desired to follow this guideline for its project.
The purpose of the regulations is to ensure safety and integrity of the marine vessel, facility, and personnel during the loading operation. The regulations deal with issues such as fire, explosion, over and under pressure, and overfill of marine vessels.
The regulations do not require installation of a vapor-control system, but instead dictate the safety equipment that must be installed if a vapor-control system is used. The environmental authority in a state or country will dictate whether vapor control is required for an application.
In marine vapor combustion systems, safety begins at the dock.
Each system typically includes one dock safety unit for each dock in which product will be loaded. This unit consists of safety equipment to protect the vessel from fire, explosion, over and under pressure, and overfill.
For ease of installation, this equipment is typically packaged on a skid. For this particular application, much of the equipment was already installed because the facility was already utilizing vapor control.
The adsorption system that was installed was considered vapor-recovery technology by Coast Guard regulations. Because the design requirements for vapor-recovery systems and vapor-combustion systems differ, a few components had to be added, but a complete dock-safety unit was not needed.
By utilizing existing equipment, TMPL was not only able to save money on equipment, but also on installation cost because implementing a new dock-safety unit would have meant significant rework on the dock.
From the dock-safety equipment, the vapors flow through pre-existing piping to the existing scrubber system blower. The blower discharges the vapors into the scrubber vessels and then into a second blower that was added as part of the marine vapor-control system.
The second blower is so designed that the scrubber system can be bypassed and the blower can transfer the vapors from the dock to the vapor-combustion unit.
Vapor-combustion unit
The second blower discharges into a John Zink vapor-combustion unit (VCU). There, hydrocarbons and sulfur-bearing compounds are destroyed by oxidation.
The vapor-combustion unit operates at a temperature of 1,400-1,800° F. and is designed to achieve 98% destruction efficiency of the hydrocarbons and 99% of the H2S and mercaptan compounds.
Because odors were the primary concern of TMPL in the system design, the company wanted to achieve the highest possible destruction efficiency of the H2S and mercaptans.
These compounds, however, create combustion products such as SO2 and SO3 that also can cause odors in certain concentrations. In addition, SO2 can also pose health hazards before it can be smelled. This could create occupational hazards for the workers on-site.
Therefore, to ensure that the VCU would adequately control the odors from the loading operation without creating any additional hazards, John Zink determined that dispersion modeling of the combustion products was required.
The dispersion model was also used to ensure that the combustion products would not result in emissions of SO2, CO, and NOx that exceeded the Greater Vancouver Regional District guidelines.
The first step was to determine the maximum concentration of H2S and mercaptans in the vapors discharged from the ship.
John Zink acquired samples of two or three of the crudes that were expected to have the highest concentrations. The samples were analyzed for molecular weight, ASTM distillation curve, H2S concentration, and mercaptan concentration.
A process simulator performed a flash calculation to determine the maximum concentration of hydrocarbons, H2S, and mercaptans in air. This represents the saturation that occurs between the liquid phase and the air (vapor) phase in the ship during loading.
The first dispersion model was performed by assuming that the vapors discharged from the ship would be processed directly by the VCU, without utilizing the scrubber. The vapor composition used was that determined by the flash calculation.
This model produced levels of SO2 that were greater than the odor threshold. Therefore, it was determined that the scrubber would need to be used in series with the combustor to minimize the level of H2S which would be processed by the combustor and therefore minimize the SO2.
Table 1 presents the final composition and flow rate modeled; these were developed by the flash calculation in combination with operational data from TMPL.
Table 2 shows the estimated flue-gas composition from the combustor. This is the composition that was used for the model.
Fig. 3 shows a contour plot developed from the dispersion model. This plot shows the maximum 1-hr emissions of SO2 at the fence line and also in the areas surrounding the facility.
Concentrations of other components were determined by a linear ratio of the flue-gas concentrations. Historical data revealed that the area in which the odors had been most problematic was around Cliff Ave.
The dispersion model demonstrated that implementing a vapor-combustion unit would result in ground-level concentrations of the odorous compounds less than the odor threshold in this area, as well as other neighboring communities.
The model also confirmed that the maximum concentrations of flue-gas products occur on-site, and these concentrations will be within the occupational health regulations set by the Workers' Compensation Board of British Columbia and the US Occupational Safety & Health Administration.
Installation
Once the system design was established and confirmed by the dispersion modeling, implementation of the system began.
For the design, manufacturing, installation, and start-up phases of the project, TMPL desired a turnkey approach in which one vendor would be responsible for successful completion of all phases.
This is common in this type of project in which several components make up the integrated system. It is important that the control all of the components is incorporated into a common PLC program for proper communication between the components.
A turnkey project is typically bid in a lump sum fashion and includes all phases of the project. The problem with the turnkey approach is that it is difficult to estimate the cost of the field engineering and installation portion of the work before the system design is finalized.
This forces the turnkey bidder to take responsibility for unknown risks, which typically causes an escalation of the lump sum price of the project. A more economical approach is to finalize the equipment design first, and then obtain bids for the fieldwork.
This will eliminate the unknowns and associated risk to the installer.
In order to minimize the overall cost of its project, TMPL made the decision to separate the fieldwork from the equipment supply. TMPL, however, still wanted turnkey responsibility from the equipment manufacturer.
This was accomplished through shared responsibility between John Zink and TMPL. John Zink was contracted not only to design and manufacture the equipment but also to participate in the field installation.
The company was responsible for the design of the field-installed piping. In addition, it was responsible for putting together procurement packages for the field engineering and construction companies.
TMPL and John Zink jointly reviewed the bid packages and selected the best vendors for the project. John Zink reviewed all field drawings to ensure that the equipment information was correctly incorporated into the drawings.
Lastly, the company performed field inspections of the installation and commissioned the system. TMPL procured the fieldwork and acted as the general contractor for the work. This gave it the flexibility of working directly with the contractors and helped the project run more smoothly.
Because the project was performed in a staged fashion instead of a lump sum fashion, unnecessary risks were eliminated and the overall cost was reduced.
The marine vapor combustion system was successfully commissioned in June 1999 and in July the first ship was loaded. The project was completed on time and under budget and there have been no odor complaints associated with vessel loading since the system was installed.
The preliminary design work performed on the front end of this project enabled John Zink and TMPL to optimize the system design to best meet the needs of the facility. In addition, the preliminary work ensured TMPL that the system installed would meet the GVRD requirements and would not pose any health hazards in the facility or in neighboring communities, thus securing their investment.
The authors
Melissa Lenhart is a senior application engineer in the vapor-control group of John Zink Co., Tulsa, having joined the company in 1991. Previously, she held summer positions with Mobil Oil Co. and ARCO Alaska Inc. Lenhart hold a BS (1991, cum laude) in chemical engineering from the University of Tulsa.
Kevin Savage is a senior pipeline engineer with Trans Mountain Pipe Line Co., Vancouver. He has managed pipeline facility projects and provided operating engineering since joining Trans Mountain in 1990.
Savage has worked on a variety of projects from pipeline construction, pump stations, metering facilities, water-treatment, and vapor control. He holds a BASc in electrical engineering from the University of British Columbia
