Myth 9: The pipeline often breaks down and restoring it needs time which will disrupt supply as CNG cannot be stored. So the complete dependence of publictransport on  it is bad. The city  will come to a  halt if  there is a breakdown in the only gas pipeline in the country

The Union Government has claimed that there will, however, be uncertainty over uninterrupted supply if either the gas processing plant or the pipeline fails (The Pioneer, July 26, 2001).


Fact

The possibility of the pipeline breaking down is remote. Various methods of natural gas storage have been developed to meet the demand for natural gas during shortages These methods are now technologically well established.

Natural gas can also be stored in the form of liquefied natural gas (LNG).

According to the US DOE, natural gas can be stored in the pipeline itself by increasing the capacity of the pipeline or by compressing more gas into the same space for short periods of time.

CSE experts panel report on CNG as a fuel for urban buses in Delhi states, “In our view, the chances of a disruption of gas supply that could shut down the public transport fleet are remote. Gas pipelines are highly reliable, and are designed to be able to continue in operation at reduced capacity even if there were failure in, for instance, a pumping station. Further, the pipeline and distribution systems themselves store a considerable quantity of gas, as would the CNG tanks of the buses themselves. Appropriate contingency plans should be put in place to assure that buses would have first priority in access to this gas in the event of a supply disruption.”71

“Although the chance of a prolonged disruption in gas supply is remote, such an event would have serious consequences for public transport. To guard against this possibility, we suggest that the cognisant authorities consider establishing gas storage facilities.”72

The demand for natural gas can sometimes exceed the amount that can be supplied through a pipeline on a daily basis and during certain periods of a year. In countries like the US this is seen during the winter when demand for gas for room heating increases sharply. To meet this demand various methods of natural gas storage have been developed and the storage methods are now technologically well established.

A large amount of natural gas is stored in the US today. The three principal types of underground storage sites used in the US are:
1.    Depleted reservoirs in oil or gas fields: This is by far the most prevailing type of storage. These are usually located close to the centres of consumption.
2.    Aquifers: An aquifer is suitable for gas storage if the water-bearing sedimentary rock formation is overlaid with an impermeable cap rock.
3.    Salt cavern formations: This is a more costly option than the other two.73

In 2000, there were 348 depleted gas/oil reservoirs, 40 aquifer and 27 salt cavern storage sites for storing natural gas in the US. The total amount of natural gas stored that could be delivered was 77,734 million cubic feet (equivalent to 2,201 million cubic metre) per day.74

Alternative methods of natural gas storage
1.    An alternative method for on-site storage of natural gas is to store it in the form of LNG. A possible alternative source of CNG for transport fleets is to build (or obtain access to) a fuelling station where CNG is dispensed from LNG that is stored on-site. This is done by using high-pressure cryogenic pumps to compress the LNG to 4,000-4,500 pound square inch (psi, equivalent to 276-310 bar) and then vaporising the highly compressed liquid.75

This method offers several advantages over conventional CNG:
a)    Cryogenic pumps require significantly less energy than the compressors used at the conventional CNG stations and are less maintenance-intensive.
b)    Since LNG is essentially pure methane, LNG or CNG is delivered to the vehicle with virtually no contaminants or undesirable fuel elements such as oil carryover, moisture and higher hydrocarbons. This eliminates the need for elaborate gas drying and filtering systems.

According to the US-based Gas Research Institute, the capital costs of a large (2,000 standard cubic feet per minute = 3,398 cubic metre per hour) LNG or CNG station can be nearly 50 per cent lower than a conventional CNG station. Operation and maintenance cost can also be significantly lower.76

The CSE experts panel on CNG points out in their report that “Many gas utilities in the northern US have set up gas liquefaction and vaporisation facilities to help them meet peak wintertime gas demands. During off-peak periods, these facilities convert part of the incoming pipeline gas to LNG, which is stored in large insulated tanks. The LNG is then re-vaporised in and injected into the gas distribution system to meet peak demand. A similar facility could be used to assure continuity of essential gas supplies to Delhi in the event of a prolonged disruption in pipeline activity.”77

“The presence of a LNG backup system could also help in other ways. LNG can be used as an alternative to CNG for storing gas on-board vehicles, and has many advantages over CNG for heavy-duty trucks and long-haul buses (in particular, more fuel can be stored with less penalty in increased weight). Systems for converting LNG to CNG have also been developed. These have the advantage that the LNG can be pumped up to the dispensing pressure of 200 bar as a liquid, and then vaporised under pressure to produce CNG. This eliminates the need for a compressor at the dispensing station. Transporting gas to off-pipeline stations as LNG and then dispensing it as CNG would have many advantages over the present arrangement of mother and daughter stations — specifically, more gas could be transported over much longer distances, making it practical to provide CNG over a wider geographic range, and even in surrounding cities not served by the gas pipeline,” points out the experts’ report.

2.    Storage in pipeline: According to the US DOE, pipelines can be another place for storage of natural gas. This can happen either by increasing the capacity of the pipeline or by compressing more gas into the same space for short periods of time. The second alternative is called line packing.78

3.    Theoretically, natural gas can also be stored in the form of hydrates. This requires freezing the gas in presence of water. When frozen in presence of water, natural gas produces a stable compact structure that can be quickly thawed as needed to retrieve the gas. Some 181 standard cubic feet of gas can be stored per cubic feet of hydrate.79