What is causing the Hum ?

Natural Gas Compressors and Pipelines

Natural Gas

The continental United States alone has more than 210 pipeline systems that are made up of 490,850 kilometers (305,000 miles) of transmission pipelines that transfer gas to all 48 states. This system requires more than 1,400 compressor stations to ensure that the gas continues on its path, 400 underground storage facilities, 11,000 locations to deliver the gas, and 5,000 locations to receive the gas. This does not include gathering systems

Almost 100 Countries 

Natural Gas production occurs in almost 100 Countries with the 20 biggest producers being

1  USA
2  Russia
3  Iran
4  Qatar
5  Canada
6  China
7  Norway
8  Saudi Arabia
9  Indonesia
10  Turkmenistan
11  Algeria
12  Australia
13  Malaysia
14  United Arab Emirates
15  Uzbekistan
16  Netherlands
17  Nigeria
18  Argentina
19  United Kingdom
20  Trinidad and Tobago

Compressor Unit

The compressor unit is the piece of equipment which actually compresses the gas. Some compressor stations may have multiple compressor units depending on the needs of the pipeline. The compressor unit is a large engine which typically works in one of three ways:

Turbines with Centrifugal Compressors – This type of compressor is powered by a turbine to turn a centrifugal compressor and is powered by natural gas from the pipeline itself.

Electric Motors with Centrifugal Compressors – This type of compressor also utilizes centrifugal compressors to compress the gas; however, instead of being powered by a natural gas fueled turbine, they instead rely on high voltage electric motors.

Reciprocating Engine with Reciprocating Compressor – This type of compressor uses large piston engines to crank reciprocating pistons located within cylindrical cases on the side of the unit. These reciprocating pistons compress the gas. These engines are also fueled by natural gas.

Frequency of Compressor Stations

The total number of compressor station facilities required to move product varies depending on the region and conditions. Generally compressor stations are located about every 40-70 miles along the pipeline.

Operating Pressure of Natural Gas Pipelines

There is a wide variation in the pressure within a given section of pipeline compared to other pipelines in other areas. The typical pressure may range anywhere from 200 psi (pounds per square inch) to 1,500 psi. This wide variation is also due to the type of area in which the pipeline is operating, its elevation, and the diameter of the pipeline. Because of the change in the environment, compressor stations may compress natural gas at different levels. Supply and demand can also be a factor at times in the level of compression required for the flow of the natural gas.

Pulsations generated by Compressors

Pulsations can be generated by reciprocating compressors, centrifugal compressors, flow induced phenomena, or turbulence.
A reciprocating compressor produces pulsation at compressor  crankshaft  RPM  and  its  multiples.    Pulsation frequencies are generally  expressed  in  cycles per  second  (Hertz).  A  300-RPM  compressor  produces pulsation at 5 Hertz, 10  Hertz, 15  Hertz,  and  higher  multiples.  Most compressors  (for  natural  gas  services)  are  double-acting  and  compress  gas  on  the  head and  crank end of the  cylinder.  Double-acting cylinders produce more pulsation at the even multiples of RPM and less at the odd multiples.

Historically,  designs of centrifugal compressor  systems have focused on the aerodynamic and  performance aspects.  Noise, pulsation, and vibration phenomena were rarely considered.  Several transmission system failures, in different gas transmission companies, were documented. They included fatigue failures of the compressor components, piping attachments, and, in some instances,  pipework  shell failures. As a result, numerous investigations were carried out While the compressors were adequately designed from the aerodynamic performance  point of view, they appeared to act as dynamic generators, producing excessive noise, pulsation, and vibration  levels even when operated well within their design parameters. It was found that neither the designers nor equipment users had a clear understanding on how  to practically analyse and  mitigate such dynamic phenomena.

Many gas transmission system designers, some working for world renowned consulting firms, do not  consider  it necessary to dynamically  design  compression  facilities incorporating centrifugal compressors. They reason that such machines cannot cause unacceptable pulsation and vibration problems similar to those observed  in  reciprocating compressors. Hence, a standard opinion prevails  that  the use of  centrifugal compressor  eliminates acoustical vibration problems. How wrong this statement is, only the owners and operators of high flow gas transmission systems can testify. Frequently, numerous operational problems and equipment failures begin to surface at a compression facility within  100 to 2000 hours  of  operation.  They  include  failure  of  piping  or  compressor components, unscheduled outages as well as noise related environmental  complaints.

Components  of  Noise and  Pulsation  Generated  by  Piping  
Systems

Noise and pressure oscillations  in piping  systems are caused by flow turbulence, increased  turbulence  due to discontinuities in flow path  (flanges, thermowells,  valves),  internal acoustic field response, and transmission of mechanical vibrations into the piping through its walls. 

Conclusion

Natural Gas Compressors and Pipelines can and do create noise and pulsations. The degree of noise and pulsation varies with the particular design of the Compressors and Pipelines. Considering the proliferation of natural gas production and the sheer number of natural gas compressors in the world today, they must be considered as a possible source of the Hum heard around the world.

Our research in particular has reasonably eliminated all other sources as possible sources of the world Hum including Airports, Freeways, Trains, and Wind Turbines. We believe that Natural Gas Compressors and Pipelines are the source of The Hum heard around the World to the exclusion of all other reasonable explanations.