Dr. Jesse Yoder, founder of Flow Research and respected industry expert, discusses accurate measures to manage gas flaring in the light of climate change as well as health and safety.

One of the most important issues being addressed on a

worldwide basis by multiple governments is the issue

of global warming. Global warming is not just the idea that the earth’s temperature

is slowly increas-ing over time; it is specifically tied in

with the idea that this increase is caused

by certain chemicals released into the air as

a result of human activity. Global warming used to be

a scientific theory that was hotly debated by both scientists

and by many people who

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were concerned with the potential for long-term damage to

the environment. At the same time, there were

some who felt that the evidence that any temperature increase is occurring was either coincidental, or a natural result of the evolution of climate change.

Global Warming Now an Accepted Fact

This debate is largely over today, due to the

overwhelming evidence that the oceans are slowly getting

warmer, the polar icecaps are

Measuring, Flaring, and Venting of Natural Gas in Oil and Gas Environments

INDUSTRY: OIL & GAS PUBLISHING DATE: JUNE 2016

melting, more violent and destructive storms are becoming commonplace, and the average annual temperatures in many locations are increasing each year and have been doing so for at least 10 – 20 years. In the face of such overwhelming evidence, the number of people who do not accept the reality of global warming at this time is very small.

Global warming is of major concern to those in the oil & gas industry. There are many sources of green-house gases and pollutants that damage the atmosphere, but a significant portion of these are associated with oil and gas production, refining, and with petro-chemical plants. Greenhouse gases are any gases that contribute to the greenhouse effect by absorbing infrared radiation, e.g., carbon dioxide and chlorofluorocarbons.

The Greenhouse Effect and Greenhouse GasesThe greenhouse effect is best understood as a result of the warming of the earth by the sun. The earth is constantly subject to large amounts of radiation, mainly from the sun. This radiation takes the form of visible light, ultraviolet light, infrared radiation, and other types of radiation. According to the National Aeronautics and Space Administration (NASA), about 30 percent of the radiation reaching the earth is reflected back into space by clouds, snow, sand, ice, and other reflective surfaces. The remaining 70 percent of this radiation is absorbed by the land, the ocean, and the atmosphere. The absorbed radiation causes these surfaces to heat up, and to release heat in the form of infrared radiation.

Some of the infrared radiation that is released by the earth’s surfaces passes into outer space. However, some gases actually absorb this infrared radiation and prevent it from passing into space. These gases are called greenhouse gases because they work somewhat like a

greenhouse in trapping infrared radiation. It is difficult for infrared radiation to pass through the glass walls of a green-house, resulting in the warming of the green-house. Likewise, greenhouse gases absorb the infrared radiation reflected by the earth’s surfaces, preventing it from escaping into

outer space. The net effect of this absorption of infrared radiation is the gradual heating of the earth’s atmosphere, and is called global warming.

The Kyoto Protocol identifies six of the main greenhouse gases:• Carbon dioxide (CO2)• Methane (CH4)• Nitrous oxide (N2O)• Hydrofluorocarbons (HFCs)• Perfluorocarbons (PFCs)• Sulphur hexafluoride (SF6)

Regulations Governing Gas Flaring and Venting of GasesAs a result of their harmful effect on the atmos-phere, the Environmental Protection Agency (EPA) in the United States has undertaken to limit the amount of harmful compounds that can be released into the air. The initial regulations to address this problem began with the Clean Air Act of 1990. In Europe, the European Union

Engineers working on an offshore platform with an active flare stack.

tures occur, releasing gas to the safety system of venting or flaring prevents potential harm to employees or to the public. It is also sometimes necessary to dispose of natural gas contami-nated with drilling mud or acids.

Flaring vs. Venting of GasesWhile gas is often flared, sometimes it is just vented to the atmosphere without being flared. The emissions that result from either process

depend on multiple factors, especially the combination of the gas being vented or flared. The gases emitted

from offshore platforms are typically methane, along with other hydrocarbons, hydrogen sulfide, and smaller amounts of inert gases. The gas emitted from onshore facilities tends to be somewhat more complex.Flaring of gas is generally considered to be less environmentally harmful than venting of gas. The main reason for this is that natural gas (methane and associated gases) has a much greater effect on global warming than CO2, which is produced by flaring. Estimates are that a kilogram of methane has 21 times the global warming potential as a kilogram of CO2. For this reason, flaring is considered to be a much more environmentally friendly way of disposing of natural gas than just venting it to the atmos-phere.

Flowmeters that Measure Flare GasInsertion turbine, averaging Pitot tube, thermal, and ultrasonic flowmeters have all been used in measuring flow in flare stacks. While all of these technologies have their merits, some are more effective than others in flare stack measure-ment.

The chief disadvantage of insertion turbine meters is that they have moving parts that are subject to wear. They also intrude into the flowstream, which puts them into direct contact with the measured fluid. Particles in the

(EU) Emission Trading Scheme (ETS) was instituted in 2005 to regulate all six greenhouse gases identified by the Kyoto Protocol; however, to date it has mainly focused on carbon dioxide (CO2).

In the United States, the Environmental Protec-tion Agency (EPA) has the authority under the Clean Air Act to request emissions data from operators of oil and gas wells and refineries. This authority is specified under federal rule 40 CFR 98 Subpart W, which includes flare emissions. One government department that regulates safety and the environment on offshore federal leases is the Bureau of Safety and Environmental Enforcement (BSEE). Onshore federal lands are regulated by the Bureau of Land Management (BLM). The BLM is responsible for over 63,000 federal onshore oil and gas wells. EPA Final Rule CFR, Part 60, applies to refineries with new or reconstructed flare systems, or those built or modified after June 24, 2008.

The European Union Emission Trading System is a mandatory regulation that sets limits on the amount of greenhouse gas emissions from energy-intensive installations. It applies to installations that emit CO2 such as combustion plants, power stations, oil and gas facilities, and iron and steel works. Operators of these facil-ities must comply with the EU ETS Monitoring and Reporting Regulations. The CO2 emission from a flare system is determined by calcula-tion. Most importantly, the volume of gas flared is measured. Then the amount of CO2 produced by combustion is determined through the use of an emission factor and an oxidation factor.

The Need for Flaring and Venting of GasesFlaring and venting of gases is absolutely necessary for safe operation in oil and gas production. It may be necessary in emergency and shutdown situations. When gas cannot be used commercially or stored, venting or flaring reduces the risk of fire or explosion. In cases when abnormally high pressures or tempera-

Flaring and venting of gases is absolutely

necessary for safe operation in oil and gas

production.

flowstream can potentially damage the rotors of turbine meters. Another drawback is that they are limited to a turndown of about 10:1. This limits their ability to measure both low flowrates

and high flowrates, using the same meter. This is important,

since the speed of the flow can vary signifi-cantly with both pressures and gas composition.

Like insertion turbine meters, averaging Pitot tubes have a limited turndown of about 10:1. They are also subject to clogging due to particles in the flowstream. While they are less intrusive than turbine meters, they also need to be installed in the flowstream.

Thermal flowmeters have been used effectively in measuring flow in flare stacks. Their chief disadvantage is that in order to measure flow effectively, the composition of the gas being measured must be taken into account. In terms of turndown ratios, some are capable of turndowns of 1000:1 when calibrated on air or natural gas. Like insertion turbine meters and averaging Pitot tubes, they are an intrusive form of measurement.

Ultrasonic flowmeters have significant advan-tages over insertion turbine meters, averaging Pitot tubes, and thermal flowmeters. Ultrasonic flowmeters are not intrusive, since they make their measurement by computing the differ-ence in “transit time” of ultrasonic signals sent with the flow, as compared to signals sent against the flow. Ultrasonic flowmeters do not have moving parts that are subject to wear. In addition, their turndown ratios are as high as 2000:1. This gives them the ability to measure both very low flowrates and very high flowrates. Unlike vortex flowmeters, which have a “blind spot” at very low flows, ultrasonic meters for flare gas can measure flows as low as 0.03 meters/second. The turndown of a particular meter will vary with process conditions, signal resolution, pipe Reynolds number, and other factors.

Dr. Jesse Yoder, founder of Flow Research, has been working in process control since 1986. Having advised most of the top flowmeter suppliers on market and product strategies, he has written over 160 market studies and more than 200 technical articles on instrumentation.

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Compared to venting, flaring is considered to be a much more environmentally friendly way of

disposing of natural gas.