Gazpack - Model Sulaway® - Flare gas recovery system
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How our Sulaway® system works
The next step is removing H2S from the gas in a tower filled with the adsorbent Sulabead®. This adsorbent adsorbs H2S at ambient temperature. The other tower is regenerated by heating the system to a temperature above 100°C and gas is purged into a collector from which gas is blown into a U-tube and burned up to 900°C on the end of which we inject water where H2SO3/4 is created. The injected water is collected from different drain points upstream of the process.
When heavy hydrocarbons such as siloxane are present a guard tower is mounted before gas flows into the membranes.
The next step is CO₂ removal by use of membranes. In the first stage, gas is upgraded to the next stage and a mixture of CO2/CH4 is permeated and inserted back into the inlet of the compressor, in the second stage green gas is produced that is according to required Wobbe index (44-55 mJ/Nm3).
The permeate produced at the first stage is CO₂ gas suitable for green house growing.
For CO₂ removal several methods are available:
- Growing trees: Most successful and sustainable method.
- Injection in green houses
- Liquefaction
The permeate gas from the first stage membrane is compressed up to 55 bar(g) and led into the condenser which liquefies the CO2 gas at 11° C. The liquid CO2 is boosted up to a pressure of 150 bar(g) for the bottle distribution station.
District Heating
Both packages are chilled water cooled for creating a high efficiency of all apparatus in the process line from compressor reverser up to membranes. This system creates hot water for district heating through a heat pump water chiller.
Purity Control
We have two stage membranes CO2 for upgrading of CH4. In the first stage the CH4 content is increased from 55/65% up to 62/72% depending on inlet percentage. In the second stage final percentage will be reached according to Wobbe index requirement by controlling the CO2 value between 2 and 10, whatever is required.
Sulaway® Advantages
- Impregnated Molecular sieve (Sulabead®) instead of active carbons, which means lower maintenance and transportation costs
- Production cost low due to the regeneration of Sulabead®
- Low carbon foot print due to absence of extremely polluting active carbon
- No water required nor wasted water to clean
- Drain water is used for production of Sulphuric acid (H2SO4)
- At high H2S concentrations the acid production will be profitable
- The complete process is liquid glycol cooled to obtain highest efficiency
- The heat from the chiller can be used for district heating and is higher than the electrical power consumed due to condensation heat of the drainwater
- Low power consumption
- Maintenance costs are low due to the long life to the adsorbent and compressor
- Due to intensive water removal upstream - no aggressive liquid acids: H2CO3 and H2SO3 - and water-cooled oil cooler, there is a long oil change interval
- The production costs are low due to absence of wastewater or coal
- For maintenance shut down CO2 is used as a safety gas instead of Nitrogen for two reasons: CO2 is ample available and keeps smoke gas free from Nitrogen impurities
Sustainable friendly to a Sulphur Digester
In our biogas gas plant the flare gas enters the bottom of the U tube and is ignited by a pilot light fed with propane gas. The flare is bended over 180 degrees and temperature rises up to 1000 °C. At this temperature the H2S is converted into SO2. The gas is cooled down by injection water to transform SO2 into SO3, which is solvable in water and makes Sulphuric acid (H2SO4). H2SO4 has many applications in distributing environment for production such as battery water, production of gasoline, tanning of leather, detergents etc.
Flaring on offshore platform
A responsible way to shut down flares without pollution
The bended flare quencher is the best solution for all gasses with a significant H2S content. Although the design has been proved in past studies, we have a demonstration unit ready to prove suitability for every gas composition.
On a platform
To meet the Marpol specifications the acid SO2 water is mixed with ocean water before it returns to the sea.
Nitrogen purged stack
Gas compressors have a labyrinth sealing on both shaft ends to avoid gas leakage in to the atmosphere. On the contrary to mechanical seals - applied in pumps, diesel engines and most rotating machines - labyrinth seals are not leak proof. There must be constant venting of the system. For oil free air screw compressors, leakage of air is not harmful, but for gas compressors leakage of natural gas would be harmful to the environment. For safe operation, gas is fed into a stack at safe distance from the oil/gas platform.
The solution to this problem is to shut off the gas purge and connect a nitrogen feed. This is a cheap solution as only small flows are required. The quantity of energy required for compressed air to produce nitrogen is less than gas lost in the compressor. So this is a win-win situation.Airpack is supplier of complete (small) Nitrogen packages to improve the environment.The end result for gas companies is that they save on gas leakage, which means saving money but also improving their carbon footprint.
Odorizing unit
Methane is odorous
A leakage in our gas cleaning system will not be noticed, because methane is odorless and therefore will not be detected in its natural form. Inside the Sulaway enclosure a detecting camera is mounted to detect any deformities in the passing gas and can sound an alarm. For environmental purposes the process enclosure is ventilated up to the gas cleaning filter of the flue gas chimney.
The treated (RNG) is odorized up to 16 mg/m3 thiolan (C4H8S). This is a gas with an unpleasant odor warning for leakage of gas pipes, furnaces, etc. Less costly is to use the Sulaway cleaning package and lower the H2S content to 15 ppmV. However most customers want to do the odorizing by a third party, which is called the gate keeper. The keeper checks the Wobbe index and the end client prefers a H2S content lower than 15 ppmV most of the times. The Wobbe index is a combustion indicator; the higher the value the more heat can be generated.
The HMI dashboard is placed in a ventilated enclosure. The controller consists of a gas plunger pump to supply to the controller. The electronic controller is suitable for proportional to flow control or time based flow and has a Modbus for remote communication. The enclosure will be placed on an open frame with an odor tank for liquid thiolan or equal quality. The package must be placed under a roof and for high ambient temperatures, an air-conditioned cooler is required in the enclosure.
Time based flow injection is possible at constant flow, but most packages have a fluctuating supply for which flow measurement and control is available. A sniffing line is necessary for checking the correct odor level.
Catalyst polishing
This process is designed to sweeten small sour gas flows. The catalyst is an absorbent which removes H2S. Iron water is a waste product of a sewage plant. Gazpack has developed, in co-operation with manufacturers of sewage plants, an application that transforms the iron water into granular beads. These beads absorb the H2S from sour gas. Fe2O3 + 3 H2S to Fe2 S3 + 3 H2O. The process is not reversible and creates heat during absorption.
The package consists of one compressor, a cooler, a scrubber and two towers with Sulago ® beads.
To operate successfully the following precautions are necessary.
Design criteria:
- Diameter (low contact speed causes insufficient absorption).
- Height (crushing pressure)
- Two vessels (heat transfer)
- Stainless steel (hot H2S + H2O is aggressive)
- Drain water is acid, toxic and explosive in contact with water (dangerous: add water not inverse).
This system is suitable for small capacities
Production costs are high due to:
- The saturated absorbent is a chemical waste product and processing it as such is expensive.
- Cleaning of the vessel is dirty and risky work, environmental precautions are required.
- Price per kilo is high.
The waste absorbent is toxic and is easily flammable and should be stocked under a nitrogen blanket.
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