December 1, 2008
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Home / Issue Archive / 2008 / September #9 / Nitrogen Plants and Retardation Systems: Development and Application Experience

№ 9 (September 2008)

Nitrogen Plants and Retardation Systems: Development and Application Experience

Currently, the issue of ensuring fire and explosion safety at oil  and  gas, chemical and petrochemical facilities, as well as at other industrial enterprises has become increasingly topical due to more frequent emergency situations.

By Krashennikov Yevgeniy Gennadyevitch, GRASIS and Yelansk Yevgeniy Alexanrovitch, GRASIS

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Currently, the issue of ensuring fire and explosion safety at oil  and  gas, chemical and petrochemical facilities, as well as at other industrial enterprises has become increasingly topical due to more frequent emergency situations. It is  common knowledge that it is easier to prevent fires and explosions than to respond to the consequences afterwards.
The most crucial aspect of fire and explosion safety is prevention itself. Combustion represents rapid oxidation reaction, which is conditioned by the availability of oxygen in the atmosphere, as well as by any ignition source – a spark, an electric arc or a chemical reaction with considerable heat buildup. That is why one has to stop the reaction to terminate combustion.
Establishing non-reactive gaseous medium within production facilities is the most reliable and tested way of preventing fire and explosion when performing various operations. When a gaseous medium is diluted with inactive gas and oxygen concentration goes down to 8-12 percent, combustion of the overwhelming majority of substances is becoming impossible. Such substances include the following hydrocarbons: methane, ethane, propane, benzine, kerosene, natural gas, as well as many others.
Until recently, to produce nitrogen for diluting air and establishing retarding concentration cryogenic facilities has been used. These cumbersome and expensive units were producing liquid nitrogen. Unfavorable weight and dimension parameters of such air-separating equipment, as well as its maintenance complexity rendered using nitrogen at remote facilities expensive and restricted. Cryogenic facilities allowed for producing only liquid nitrogen with the possibility of its subsequent gasification and filling it into gas cylinders under a pressure of 150 atm. As transporting both cylinders containing gaseous nitrogen and tanks containing liquid nitrogen was rather complicated, the bottom-line cost of nitrogen went up considerably.
An alternative method of producing gaseous nitrogen fraction based on pressure swing adsorption technology, which appeared later, did not allowed for reducing prime cost of produced gas. One of the drawbacks of PSA systems was their relatively low dependability and considerable dimensions, which prevented installing them at remote facilities and small-size enterprises. Since oil-and-gas facilities required space-saving self-contained mobile systems suitable not only for rapid deployment at the site, but for operation under the most severe climatic conditions, the adsorption-based systems received no wide recognition.
A technological breakthrough in nitrogen production occurred in early 1980s, when membrane systems were introduced into industrial application to produce nitrogen from atmospheric air. Having low dimensions and weight, as well as minimum requirements to air-preparation quality, and being resistant to vibration and impacts, membrane-based systems rapidly enjoyed wide recognition in economically developed countries. Due to their high dependability and compact size, all the mobile nitrogen-production plants are manufactured on the base of membrane gas-separation technology.
Schematically, the method can be described as follows. Air pumped by a compressor is delivered to a gas-separation unit, where nitrogen is released. A gas-separation unit consists of membrane cartridges, each of which is a polymer membrane in a metal case. A cartridge is manufactured of a cluster of synthetic fibers allowing for separation of gaseous mixtures. Due to fiber parameters, gases contained in the air penetrate a membrane with different velocity. As a consequence, nitrogen is released from the air delivered under pressure. The purity of nitrogen produced is from 90 percent to 99.9 percent and above.
Since there is not any motion work, nitrogen membrane facilities proved to be exceptionally dependable and easy-to-use, at the same time having low dimensions and no maintenance costs. These and many other advantages of membrane systems allowed for launching production of stationary nitrogen plants and mobile nitrogen stations, which are drastically different from the existing systems in terms of their cost-performance characteristics.
It hasn’t been until recently that the operation of such systems started in Russia and in CIS countries. This delay was first of all connected with the high cost of the foreign-made counterparts, as well as with the absence of flexible approach to the customer’s requirements.
Up-to-date stationary membrane systems used to produce gaseous nitrogen and installed at various industrial facilities (starting from chemical and petrochemical ones and down to oil-and-gas enterprises) enjoyed really high appreciation with the operating organizations. This is also true for nitrogen stations ensuring safety at remote oil-and-gas production and processing facilities.
Nitrogen is an indispensable component of numerous production processes in oil-and-gas industry. Nitrogen plants and stations are used to ensure fire and explosion safety during transportation, transshipment and storage of hydrocarbons, as well as for testing, purging pipelines and process vessels of explosive vapors accumulated in them. Nitrogen is used most extensively in oil-and-gas industry. This usage is governed by several categories of regulations: “Safety Regulations in Oil-and-Gas Industry” RD 08-200-98, “Regulations for Operation, Inspection, Repair and Rejection of the Field Pipelines” RD 39-132-94, “Industrial Safety Regulations for Oil Refining Industry” PB 09-310-99, “General Regulations of Explosion Safety for Explosion Hazardous Chemical, Petrochemical and Oil Refining Enterprises” PB 09-170-97. Some extracts from the above-mentioned regulations concerning application of gaseous mediums during repairwork and preventive maintenance are cited below.
In accordance with the requirements towards safe operation during production, gathering and treatment of oil, gas and gas condensate, oxygen contents should not exceed 1 percent (vol.) when purging CPF processing vessels. After purging equipment and pipelines both prior to initial start-up and after repairwork which involved opening equipment and pipelines, residual oxygen content should not exceed 1 percent (vol.) Before regenerating catalyzer, a reactor block system should be emptied of liquid petroleum products and purged with inactive gas until the contents of combustible gases in the systems is no more than 3  percent (vol.)
Nitrogen facilities are employed in chemical and petrochemical industries to purge and protect processing vessels with inactive gaseous medium in order to ensure fire and explosion safety. Nitrogen systems are also used for testing pipeline systems, transporting chemical substances, regenerating catalyzers and in many other technological processes. In paint and varnish industry the nitrogen systems are applied to create retarding concentrations in processing vessels. Nitrogen production systems are also used in packaging and for displacing oxygen to prevent polymerization of bodied oils.
Nitrogen plants are stationary units used to produce gaseous nitrogen. These plants allow for producing 5 to 5,000 ncu.m/h of nitrogen with the purity from 90 percent to 99.965 percent, i.e. using these plants it is possible to produce both Azotan (gaseous fire-extinguishing agent) and Grade 1 utility nitrogen, in accordance with NRB 88-2001 regulation. It is worth mentioning that in most cases 90 percent of nitrogen is enough to establish retarding concentration, i.e. reliably prevent combustion.
Producing Azotan and utility nitrogen by means of nitrogen stations turns out to be the cheapest of all gaseous fire-extinguishing agents. Azotan costs about 30 copecks/ncu.m (a cubic meter at standard conditions), while utility nitrogen costs about 1 ruble/ncu.m. A wider recognition of these compositions has been restricted by the underdevelopment of regulatory framework.  A certain work is underway in this aspect and some supplementary instructions and documentation is being developed at present.
However, even now up-to-date membrane-based nitrogen units are finding ever-widening application in preventing fire, creating fire-extinguishing and retarding concentrations by means of displacing oxygen from air in quite a number of industries. As of now, the economic feasibility of using nitrogen membrane systems in oil-and-gas, chemical and petrochemical facilities, as well as in other industries advisability, is beyond any questions. Using nitrogen membrane plants leads to considerable cost cutting at an enterprise, and, which is more important, allows for preventing fire and inflammation at industrial facilities.

Krasheninnikov Yevgeniy Gennadyevitch, Ph.D. in physics and mathematics, Engineering Director, GRASIS.

Yelansky Yevgeniy Alexandrovitch, Marketing Director, GRASIS.

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