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HPInnovations

10.01.2011  | 

Keywords: [Mercaptan destruction] [pipeline waste] [membrane bioreator] [wastwater treatment] [filtration] [lubricants] [high-quality fuels] [hydronic boiler] [biodiesels]

Mercaptan oxidation in aqueous waste

 

  Fig. 1. Mercaptan destruction rate.  

Tert butyl mercaptan (TBM) and dimethyl sulfide (DMS) are oxidized to destruction in an aqueous-waste solution containing methanol (MeOH), monoethylene glycol (MEG), ammonia and hydrocarbon sources using advanced oxidation process (ozone, hydrogen peroxide and uV). The aqueous solution in the trial mimics the expected waste stream from a gas-transport pipeline.

Background to the problem.

PSE Kinsale Energy required a process to dispose of an aqueous waste stream in a gas-storage project. Injection gas constitutes odorized natural gas containing 4.7 ppmv and 1.3 ppmv of TBM and DMS respectively. This is injected into an offshore reservoir during summer for winter withdrawal. Withdrawn gas is expected to be water saturated, and hydrate inhibitors, MEG and MeOH, are injected. The aqueous waste generated from the onshore separator contains MEG/MeOH, TBM/DMS and trace amounts of native petroleum species (alkanes, cyclics, phenol, etc.).

Initial treatment options.

Due to the uncertainty of produced water flowrates (from 10 m3/d to 100 m3/d) and the relatively low absolute value of flows, disposal is best achieved by third-party offsite disposal. Third-party water-treatment plants cannot accept a waste with mercaptan (thiol).

Pilot-trial results. Phase 1 of trials by PSE Kinsale Energy was to establish background rates of MEG/MeOH destruction. If the process achieved significant MEG/MeOH destruction, disposal could be implemented within the site and transport infrastructure could be avoided. Batches ran up to two hours. Achieved destruction for samples of different chemical oxygen demand (COD) concentrations, respectively 98 mg/l and 35 mg/l, were 45% and 12%. This did not yield a viable disposal process and was unexpected.

Phase 2 dosed mercaptan and petroleum species into MEG/MeOH solutions. The trials were located in a remote area due to odor potency. Vials were opened under a liquid surface to prevent gas escape, and equipment was rinsed with hypochlorite to destroy mercaptan odor. The trial equipment was placed under a fume-hood with an extract fan fitted with a KOH/KI-impregnated activated-carbon filter.

In tests, mercaptan odor was not evident after 30 minutes. Subsequent trials with varying solution strengths confirmed this. Increasing the background COD from 700 mg/l to 2,400 mg/l equivalent did not significantly affect the mercaptan destruction rate as detected by the trial operators, as shown in Fig 1.

Attempts to identify a rate of reaction were not possible; the reaction was quicker than one simple residence time (50 liters circulated at 1m3/h).

In Phase 3, two batches of a fully simulated waste with petroleum species were processed for 120 minutes. The analysis to confirm odor destruction was three-fold:
• Liquid samples were taken at time intervals and analyzed for mercaptan.
• After 120 minutes, the batch was transferred to a barrel for headspace analysis using graphite adsorption tubes.
• Liquid samples were taken at time intervals and subsequently sampled by an odor panel. Mercaptan destruction was confirmed within 60 minutes.

Conclusion.

The advanced oxidation process using ozone/uV rapidly and selectively destroyed mercaptan in an aqueous waste containing MeOH, MEG and petroleum species. Competitive behavior was negligible despite the higher concentrations of the potentially competing species. Despite the inference in published research, the oxidation process was not capable of destroying MeOH or MEG in a time suitable for process implementation.

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Wastewater treatment exceeds standards

The result of a four-year development effort, GE’s next-generation membrane bioreactor (MBR) wastewater-treatment technology, LEAPmbr, is claimed to offer the lowest life-cycle costs available from any MBR technology, while also being cost-competitive with conventional treatment. These cost savings, along with operational simplicity and a compact footprint, derive from innovations to the popular GE ZeeWeed 500 MBR product line. Cost and efficiency savings include:
• A minimum 30% reduction in energy costs
• A 15% improvement in productivity (greater water-treatment capacity)
• A 50% reduction in membrane aeration equipment and controls, leading to a simpler design with lower construction, installation and maintenance costs
• A 20% reduction in physical footprint, leading to further reduced construction and installation costs, as well as lower ongoing consumption of cleaning chemicals.

MBR technology consists of a suspended-growth biological reactor integrated with GE’s high-performance, rugged ZeeWeed hollow-fiber ultra-filtration membranes. ZeeWeed membranes are immersed in a membrane tank, in direct contact with the water to be treated, which is known as mixed liquor. Through a permeate pump, a vacuum is applied to a header connected to the membranes. The vacuum draws the water through the ZeeWeed membranes, filtering out solids, along with bacteria and viruses. The filtered water, or permeate, can then be further treated, reused or discharged as needed.

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Alliance brings together production technology

UOP LLC, a Honeywell company, has formed a licensing alliance with ExxonMobil Research & Engineering Co. (EMRE) to offer integrated solutions for producing lubricant oils and high-quality fuels. The agreement between Honeywell UOP and EMRE will reportedly provide a one-stop solution for refiners to maximize lubricant oil and diesel fuel production levels. The alliance harmonizes EMRE technology, used to produce lube base oils for use in motor oil, with UOP hydroprocessing solutions that produce the high-quality feedstocks needed for lubricant production.

Users will also have access to integrated process design solutions for EMRE fuel-dewaxing technologies and UOP hydroprocessing solutions to produce high-cetane, ultra-clean diesel for cold climates in a single engineering package. “By bringing together these two well-established portfolios, we are maximizing solutions for our customers to produce more and better products from each barrel of crude,” said Pete Piotrowski, vice president and general manager of Process Technology and Equipment for Honeywell’s UOP.

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Redesigned analyzer for H2S in crude oil

 

  Fig. 2. Applied Analytics’ headspace system.




The OMA-300 hydrogen sulfide (H2S) analyzer crude oil edition from Applied Analytics, Inc. (AAI) is a specialized configuration of the OMA-300 H2S system. Equipped with a headspace sample-conditioning system, it monitors an opaque liquid process. When a sample is too dark or dirty to transmit a light signal, the headspace system is said to produce a representative vapor-phase sample that can be easily monitored via ultraviolet-visible absorbance spectroscopy and correlated to the chemical composition of the liquid process.

“AAI has always offered a highly effective solution for measuring H2S in opaque liquids, but the current demand for crude analysis has given us cause to rethink our offering,” said Dan Murphy, senior mechanical engineer. “The process resulted in modifications to the crude oil edition of the OMA-300 H2S. The refined design puts everything in one enclosure and adds the capability to monitor multiple crude streams at once using multiple headspace columns running in parallel.”

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Renewable fuel options for condensing hydronic boiler

  Fig. 3. Fulton’s Vantage boiler.  


Fulton’s Vantage boiler, which has been available since 2003 as an ultra-high-efficiency condensing hydronic boiler, is said to be drawing attention for its ability to use B100 biodiesel and ultra-low-sulfur (under 15 ppm) heating oils for full condensing operation. “As a result of comprehensive testing at the independent Brookhaven National Laboratory, it has been proven that the Vantage can meet or exceed the thermal efficiencies attainable with natural gas,” said Erin Sperry, Fulton’s commercial heating product manager.

The biodiesels used in the Brookhaven testing facility included biodiesels produced from both soybeans and recycled tallow. According to findings, ignition on B100 biodiesel, even from a cold start, was identical to traditional No. 2 heating oil. Testing also discovered that carbon-monoxide emissions and smoke-number readings were essentially maintained at zero during steady-state operation and at a normal excess-air level of 25%. Following test runs, burner head inspections found no significant coke deposits and measurable reductions for NOx, SO2 and soot were observed. Predicted corrosion rates were in the acceptable range for the application. Boiler-jacket loss—monitored using the standards of the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standard 103—was found to be 0.2% of steady-state input, a very low value.

At Brookhaven, boiler efficiency was measured using both an indirect flue-loss method and a direct input/output method. As typically observed with hydronic boilers, efficiency and condensate collection rate are impacted by the return-water temperature. At high fire with a return-water temperature of 122°F, efficiency was found to be 88%. At low fire with a return-water temperature of 90°F, efficiency was 93%. Under BTS-2000 test conditions of 80°F, return-water temperature and 180°F supply-water temperature, the rated efficiency was 98% at high fire.

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