Archive for April 8th, 2010
Pressure Regulator
Thursday, April 8th, 2010
Biogas Generator Benefits From Precision Pressure Control
Many wastewater treatment plants use anaerobic digestion to process their biological solid wastes, reducing landfill volumes and generating valuable electricity in the process. Controlling the biogas pressure that feeds the combustion engine is critical, especially because the flow rate coming out of the digester fluctuates. Precision back pressure regulators has been successfully used to effectively control the biogas pressure at 4 psig while circulating excess gas back to the digester for reuse.
About Anaerobic Digesters
Anaerobic digestion (AD) is a biological process in which biodegradable organic matters are broken-down by bacteria into biogas, which consists of methane (CH4), carbon dioxide (CO2), and other trace amount of gases. The biogas can be used to generate heat and electricity. The primary requirement for AD is an oxygen free environment. Other important factors, such as temperature, moisture and nutrient contents, and pH are also critical for the success of AD. Electricity can be generated on-site using a reciprocating engine, steam turbine, or gas turbine. When a reciprocating engine is used, the biogas must have condensate and particulates removed. (Source: California Energy Commission)
Anaerobic Digesters provide numerous advantages, including:
- Replacement of fossil fuels.
- Reducing or eliminating the energy footprint of waste treatment plants.
- Reducing methane emissions.
- Displacing industrially produced chemical fertilizers.
- Reducing trucking and related emissions.
- Reducing electrical grid transportation losses by generating electricity onsite.
- Reducing the volume of solid waste disposal and related costs.
- Simple and reliable systems
- Odors contained and eliminated
- Reduced operating cost
Gloversville-Johnstown’s 350KW Plant
The Gloversville-Johnstown Waste Water plant in upstate Johnstown NY, serves 25,000 residential customers, as well as 30 industrial and commercial customers. Methane from the anaerobic digester is used to fuel two 350KW Caterpillar gas engines driving generators to produce electricity, which is utilized to operate the facility. The plant processes 6 million gallons of sewage per day, and 100,000 gallons of waste is treated each day by the digesters.
In the original design, a traditional mechanical relief valve was used to control the methane pressure. This valve is designed as a safety rather than as pressure control device in that the spring that controls the relief pressure allows the valve to open completely at very little over pressure. Such a valve is necessary for the protection of the system components and safety of the plant’s personnel; however, the relief valve does not lend itself to precisely regulating the gas pressure. As a result the engines did not receive a constant pressure fuel supply and the engine rpm began to surge, something not desirable in a generator application.
A schematic depicts the original system without the gas refinement and filtering devices.
Search for precision low pressure regulator
George Bevington, the plant manager, began a search for a more precise methane pressure control strategy by contacting experts in the field of back pressure control that could configure, fabricate, assemble and ship within 10 days to complete the installation while the facility’s subcontractor crew was still on site.
Back pressure regulators work similarly to relief valves, but the emphasis is on steady state pressure control instead of on/off pressure protection.They needed back pressure regulator that uses only a frictionless flexible membrane to modulate the pressure. The inlet pressure of spring controlled back pressure regulators vary significantly with changes in process flow. In this installation, the set point is determined by a small manually operated pilot regulator (not shown) supplied with filtered shop air. The controlled pressure is in the 4 psig range. This can be adjusted to achieve optimum performance from the engine-generator system.
Stable performance
The installation of the precision back pressure regulator in parallel with the safety relief valve provided more accurate pressure control in the range required by the engines. The quick acting safety relief valve only comes into play in rare instances of excess pressure above a new higher set point. With the system pressure now smoothly controlled by the regulator and only the over pressure relief function assigned to relief valve, the pressure reducing regulators on each engine are not necessary. However, they were left in the system to avoid repiping.
Results
Tests have shown that the system can be smoothly throttled up and down the load range including taking one engine off line or running both engines wide open (700KW) with no loss of methane pressure or engine speed control.
Per George Bevington “In order to properly operate a gas compression system for anaerobic digester fueled engines, a precision back pressure regulator is needed to precisely modulate the gas pressure”.
Refining the concept for other installations:
Several changes could be made in a new installation, such as piping the relief valve exhaust to atmosphere or a flare to meet local codes. Also, the pressure reducing regulator on the gas inlet of the engine can be eliminated, simplifying the installation. With those changes the piping schematic would look like this illustration.
Conclusion:
Precision back pressure control offers a better solution to anaerobic digester gas pressure control than alternative means of controlling the pressure of biogas.
About the Author
Dave Lowles is a former executive in the semiconductor fluid controls industry. He is a consultant for Equilibar, LLC in Fletcher, NC. Learn more about
precision back pressure regulation
The right way to install a gas pressure regulator
|
|
Presto 1781 23-Quart Aluminum Pressure Cooker/Canner $79.99 The USDA recommends pressure canning as the only safe method for low-acid foods such as vegetables, meats, and poultry. The Presto 23-quart pressure canner is more than adequate for any home canning needs. It’s a professional-quality tool, made of heavy-duty aluminum, with stay-cool handles and a strong-lock steel lid. An accompanying rack fits down into the pot to keep jars up off the bottom, so … |
|
|
Presto 8-Quart Stainless Steel Pressure Cooker $68.39 Pressure cookers have experienced renewed popularity over the last several years because cooks have rediscovered what some cooks (particularly grandmas) have known for a long time–they’re really fast. And it’s easy to cook healthfully with pressure cookers, since the food retains so much more of its nutrients and flavor. Presto’s 8-quart pressure cooker is a multi-purpose pot that can stand in as… |
|
|
Prestige Popular Aluminium Pressure Cookers Prestige Pressure cookers are one the fastest and easier ways to cook any hot food. These Prestige Popular Aluminum Pressure Cookers come in a fully assembled fashion and are ideal for both home use and cooking in bulk quantities. This cooker will also come with a very detailed instructional booklet, safety valve, and manufacturer’s warranty. This cooker is easy to clean and has a heavy bottom w… |
|
|
Peerless 4-Spray/Massage Two-In-One Shower System … |
|
|
Peerless 76950 2-in-1 Shower System, Chrome $32.36 2-in-1 shower system with shower head and 4-spray hand shower. It has four selection settings: crossing spray massage, crossing spray, narrow spray massage, and narrow spray. Each item can spray separately or both can spray at one time. It has a 5-foot reinforced vinyl hose…. |
|
|
Delta Faucet 75152 Water Amplifying Adjustable Showerhead with H2OKINETIC Technology, Chrome $28.88 Offering water efficiency without sacrificing comfort, the Delta H2OKinetics Showerhead can lower your utility bills while still providing full-spray performance. This showerhead meets WaterSense criteria by offering two flow rates and two spray patterns. Its four large spray holes are engineered to be anti-clog and easy to clean.H2OKinetics ShowerheadAt a Glance:Water-saving showerhead offers low… |
|
|
Flitemate Pressure Reducing Ear Plugs $3.96 INDICATIONS: Reduces pressure in ears during flight. Remains comfortably in place for long periods. Universally made to fit most ears. Noise reduction rating 22 decibels…. |
|
|
O2 Medical Oxygen Tank Cylinder Regulator 0-15 lpm $22.99 A BRAND NEW NEVER USED CLICK STYLE OXYGEN REGULATOR Comes in sealed Manufacturers box ********0-15 LPM******* Comes in green, picture shows blue * All-metal construction provides greater durability than plastic. Anodized aluminum will not rust |
|
|
EarPlane Air Pressure Regulating Ear Plugs- Adult $5.99 EarPlanes are disposable, air pressure regulating ear plugs developed by the House Ear Institute, the leading institute in hearing research and ear surgery, and tested by the US Navy. The ear pain many travelers experience during take-offs and landing is caused by rapid changes of air pressure on the eardrum. EarPlanes slow the rate of air pressure changes There are 42 million passangers each year… |
|
|
Bayou Classic 10 psi Stainless Steel Braided Hose $19.48 So… your single – burner cooker has a “hosed-up” hose assembly? Replace it with this Bayou Classic Hose / Regulator / Valve Kit. Hose assembly toast? Replace it with this high-quality Kit from Bayou Classic. Includes 30″ high pressure hose, brass control valve and 10 p.s.i. regulator. Has 1/4″ male orifice connector. Designed for single burner cookers. High quality replacement parts from the exp… |
