The right tool for the job isn't just the right thing to do and more efficient, it can save a bunch of money. When a major shale crude oil distributor in south Texas needed to build four marine loading docks with a total system capacity of 64,000 bph and tie three of them to a vapor collection system, it turned to John Zink Hamworthy Combustion (JZHC) to provide three dock safety units, three vapor blower units, and five vapor recovery units (VRUs). To help deliver these systems, John Zink sought help from Emerson Process Management, implemented 17 of their detonation arrestors, and saved more than $900,000 compared to competing equipment. However, before that happy ending, some serious research was needed.
"Because our industry deals with volatile liquids and air, we must also handle volatile organic compounds (VOCs). And, because VOCs combine with sunlight and combustion products like NOx to produce ozone, we need VRUs and vapor combustion units (VCUs) to comply with emissions rules," said Terry McElroy, vapor control systems product director at John Zink. "The typical VRU has two tanks with activated carbon that absorb hydrocarbons from the vapor stream. While one is in the stream, the other is under vacuum regeneration.
"Meanwhile, the U.S. Coast Guard's safety standards for evaporative, hydrocarbon liquid loading are written for vessel safety, and cover over/under pressure, overfill and explosion/flashback protection. John Zink's vapor control solutions address both USCG's safety and U.S. Environmental Protection Agency regulations."
Vapor recovery and environmental regs
McElroy and Steve Attri, industrial product manager for regulator technologies at Emerson, presented "Reduce the Capital Expenditure on Vapor Recovery System Design" on the third day of Emerson Global Users Exchange 2015 on October 14 in Denver.
Established in 1929, John Zink is headquartered in Tulsa, Okla., and has 1,600 employees and 24 offices worldwide. The firm manufactures mostly process and boiler burners, flare and thermal oxidation systems, and vapor control systems, including biogas flare, vapor combustion, vapor recovery and flare gas recovery systems.
"Vapor recovery systems are a common sight these days because they're increasingly required for truck-loading, tank-storage and other applications," said Attri.
"Because vapor containing air and evaporated hydrocarbons can quickly pass through the combustible range—causing a detonation's supersonic form of combustion—McElroy reported that detonation arrestors are needed to dissipate the high-speed and destructive energy. Detonation arrestors are passive, in-line devices with crimped metal elements or equivalent heat sinks, which provide protection against flame propagation in manifolded and/or long-run piping systems.
Pressure drop savings
To ensure safe operations and mitigate damage from potential detonation incidents, McElroy stated that marine applications deploy detonation arrestors in multiple locations, typically as part of a skid-mounted dock safety unit (DSU) that also has a vapor-blower unit and a VCU. As a result, John Zink implemented 14 12-inch arrestors, one 16-inch arrestor and two 20-inch arrestors from Emerson at the shale oil distributor's three loading docks. One of the main reasons John Zink picked Emerson devices was because competing 12-inch arrestors had 102% greater pressure drop than those from Emerson, while the competing 16-inch arrestor had a 16% greater pressure drop.
"Emerson detonation arrestors limit pressure drops; keep blower discharge at or below 110°F by a thin margin; don't require ancillary equipment for vapor cooling; and don't need upsizing of detonation arrestors to limit pressure drops," explained McElroy. "By comparison, competing detonation arrestors would have needed a minimum of two 12-inch models per VRU, plus arrestors on DSU and VBU, and they would have added pressure drops."
McElroy added that if competing arrestors had been used on the safety units at the loading docks, they would have had to increase from 12-inch models to 14-inch models to handle the high pressure changes, and lines sizes on piping downstream of the vapor blowers would also have to increase. This would have cost the distributor client about $923,000 more than using Emerson's arrestors and piping.
Likewise, using competing arrestors and adding vapor-cooling equipment would have required shell and tube heat exchangers to be added downstream of four VBUs; added chilled water circuits plus associated trim from mechanical chillers; and added mechanical chiller duty.
"Emerson's low-pressure-drop solution was effectively utilized for John Zink's marine VCU," added McElroy. "The end user saved more than $900,000 by using Emerson's detonation arrestor technology, and John Zink saved more than 5% on its overall project costs."