Alyeska Pipeline starts up tanker vapor-control system at Valdez terminal

As part of Alyeska Pipeline Service Co.'s new tanker vapor-control system at the Valdez, Alas., crude-oil terminal, two new vapor-collection arms were installed on each of the controlled berths to collect vapors from tankers during loading (Fig. 1; photograph courtesy Alyeska Pipeline Service Co., Anchorage; photograph by David Predeger).

New piping was installed and integrated into the current vapor-recovery system at Alyeska's Valdez terminal to carry the vapors collected from the tankers (Fig. 2 [8,602 bytes]; photograph courtesy Alyeska Pipeline Service Co., Anchorage; photograph by David Predeger).

A tanker vapor-control system at the Valdez, Alas., marine terminal became fully operational in late March, complying with regulations that implement the Clean Air Act Amendments of 1990 (OGJ, Mar. 30, 1998, p. 39).

The terminal, operated by Alyeska Pipeline Service Co., Anchorage, is the largest U.S. crude-oil loading terminal.

The new system, which Alyeska says cost $100 million, was installed to reduce the emissions of hazardous air pollutants (HAPs) in the crude-oil vapors by capturing the volatile organic compounds (VOCs) which would otherwise be released during crude-oil loading.

The vapor-control system collects hydrocarbon vapors released during loading which are then used for balancing vapor volumes in crude-oil storage tanks or as supplemental fuel for power generation. Excess vapors are destroyed in the vapor system incinerators.

The system is the most significant change to occur at the Valdez terminal since start-up of the pipeline, according to Alyeska. It has affected virtually all of the facility's operations and maintenance activities, including its physical-plant operation and administrative procedures.

The first tanker loaded with the new vapor-collection system was the Sea River Long Beach on Dec. 12, 1997. As a result of that successful first loading, Alyeska received U.S. Coast Guard certification for Berth 4, with permission to begin practice testing of the system on Berth 5. Coast Guard certification testing for Berth 5 was completed on Feb. 9, 1998.

Formal certification of the entire system was received on Feb. 27, 1998. This early commissioning allowed Alyeska to meet the EPA compliance date of Mar. 19, 1998.

Alyeska says the project to construct and bring the vapor-control system online was completed ontime, on budget, and with no lost time accidents. Construction began in May 1996 and lasted through December 1997.

How the process works

During crude-oil loading onto marine tankers, hydrocarbon vapors are released from the crude oil as it flows into the tanker. The vapors that fill the empty tanker space are displaced as oil level rises.

The hydrocarbon vapors from the tanker are captured and piped uphill to the vapor-control system. This system also serves the 18 crude-oil storage tanks onshore.

These combined vapors are directed to three destinations:

Vapor is routed to the crude-oil storage tanks to provide vapor balancing into the space created in the storage tanks as crude oil is emptied from the storage tanks to fill tankers.

Some vapor is preferentially used as supplemental fuel to the powerhouse boilers for electricity generation if its hydrocarbon content is sufficient to burn as a fuel. Any excess vapor is routed for destruction in the vapor system's incinerators.

Alyeska says that special safety systems are provided, including those required by U.S. Coast Guard regulation, for the safe operation of the vapor system.

Each tanker's vapor space is verified to be inert (noncombustible and less than 7% oxygen) before connection to the vapor-collection system.
The oxygen content of the collected vapor is continuously monitored, and the vapor collection is shutdown if oxygen levels approach a combustible mixture.
A detonation-arresting system is provided at each berth to prevent a fire or explosion from passing through the vapor piping from shore to ship or from ship to shore.

Detonation arrestors

Detonation arrestors are installed for each berth. If sensors detect a flame (through infrared detectors) or a pressure wave, the detonation-arrestor valve closes within 50 ms. Twelve high-pressure fire extinguishers, six on each side of the valve, instantly discharge into the vapor-recovery piping, says Alyeska.

Crude-oil loading operations are automatically shutdown, and the vapor-recovery system is isolated from all other systems.

The location of the detonation arrestor valves was determined by the distance from the first detectors. The valve is located so that if a detector senses a spark or pressure wave, the valve is able to close fully before the wave will reach it, Alyeska says.

The detonation-arrestor system is unique to Valdez terminal. Other vapor-control facilities use "flame arrestor" systems. But because of the cold climate of the facility and the increased water content in North Slope crude oil, those systems would not work at the Valdez terminal, says the company.

The detonation-arrestor valves were developed for Alyeska by Fenwal.

Construction

The Valdez terminal vapor-control project required both new equipment additions and modifications to existing equipment in order to integrate marine vapor collection into the existing crude-oil storage tank vapor-recovery system.

Two new vapor arms were installed on each of the two equipped berths (Berths 4 and 5) to connect to the vapor system of the ships (Fig. 1 [12,321 bytes]). New piping was installed from the berths to connect the new system to the existing vapor-recovery system at the compressor building (Fig. 2 [8,602 bytes]).

These 24 and 26-in. vapor pipes are constructed of duplex stainless steel to provide high corrosion resistance and low maintenance, says Alyeska.

Three of the original five vapor compressors were rebuilt with new stainless-steel cases and rotors. Two of the rebuilt compressors are dedicated for tanker-vapor service and upgraded for increased capacity.

The third rebuilt compressor serves as backup for either tanker or storage-tank compressors. Two existing compressors remain dedicated for storage-tank service.

The three existing vapor incinerators were upgraded for increased capacity and the capability to burn vapors with a widely varying range of hydrocarbon concentrations because the vapors from the tankers have a different concentration of hydrocarbons than those in the storage tanks.

Regulatory role

The Clean Air Act Amendments (CAAA) of 1990 required the U.S. Environmental Protection Agency (EPA) to develop and promulgate regulations to control hazardous air pollutants based upon different types of industrial sources. EPA determined that marine terminals included significant emissions of hazardous air pollutants during the loading of marine vessels.

EPA promulgated a regulation for marine terminals, including the Alyeska Valdez marine terminal that requires the construction and operation of crude-oil vapor collection systems for the loading of marine vessels. Alyeska's compliance date was Mar. 19, 1998.

The regulations require that Maximum Available Control Technology (MACT) be applied in reducing emissions from existing marine-loading facilities which emit greater than 10 tons/year of any individual HAP or greater than 25 tons/year of all combined HAPs.

This emission reduction is defined for the Valdez terminal as a performance standard that requires tankers to be vapor tight during loading of berths with vapor controls, that the vapors in the tankers be captured in the control system, and that any incinerated vapors be incinerated within a specific temperature range.

The regulation requires two of the four berths at the Valdez terminal be equipped with vapor-collection systems. The current system of two berths with vapor-control systems is adequate to meet the current and projected requirements, says Alyeska.

Based upon an evaluation of historical, present, and projected berth operations, projections from fall 1997 indicate that throughput may be at 1.3 million b/d by 2002, as a result of new fields coming online and of increased recovery techniques being used by North Slope producers.