Some problems of gas odorization. Development of a method for neutralizing decommissioned natural gas odorant storage tanks Mixture of natural mercaptans

on the regulation.gov.ru portal there are draft amendments to air cleanliness standards. The document establishes “maximum permissible concentrations (MAC) for 13 new air pollutants.” We are talking about the air in “urban and rural settlements.” There are now more than 600 substances on this list.

Among the new ones are “sodium arsenate”, “volatile organic compounds formed during high-temperature processing of wood in the production of chipboards”, “coal dust”.

But perhaps the most interesting thing is the adjustment of the standard for mercaptans. These substances made the news in December: it was their Rospotrebnadzor that caused the stench that caused Moscow residents to suffer for several days.

As the press service of Rospotrebnadzor explained, the amendments “clarify and establish a new standard” for mercaptans. In the new version, this item is called “Odorant mixture of natural mercaptans with a mass content of ethanethiol 26–41%, isopropanethiol 38–47%, sec-butanethiol 7–13%.” And in the previous version it sounded simpler and shorter, without clarifications about ethanol and so on.

The gas leak with mercaptan is one of the reasons why Moscow was covered in a cloud of stench in December. According to ecologist Lyubov Yakubovskaya, Muscovites who contacted the 112 service were explained that a planned technological release of gas had occurred. At the same time, Mosgaz itself immediately denied any involvement in the incident.

In December, Mosekomonitoring did not record any excess of the maximum permissible concentration for mercaptans. But, perhaps, if the standard had been more clearly defined, the excess would still have been noticeable.

Mercaptans are also used in wastewater or sewage treatment plants, or, simply put, feces. So the smell in Moscow could have appeared due to a large-scale sewerage break. Perhaps a collector collapsed somewhere; according to some versions, this happened under a large-scale construction project in the Kuskovo estate.

Ethyl mercaptan, like Life, is dangerous if inhaled, swallowed, or comes into contact with skin. At high concentrations, irritation of the mucous membranes of the upper respiratory tract and eyes, nausea, dizziness occurs, and in severe cases - convulsions, drug intoxication.

Experts hope the street stench will now be better controlled.

If organizations that monitor air conditions in Moscow and other regions focus on these compounds, we can assume that the situation will improve somewhat, but the problem cannot be fundamentally solved in this way, said Evgeny Gorozhankin, an expert at the Independent Odor Measuring Laboratory.

By the way, scientists need to measure not only the level of certain substances in the air, but also the strength of the stench itself. And for this there is a special device - an olfactometer. The fact is that in most cases the smell is formed by a mixture of substances. Even if the standards for each of them are not exceeded, the stench can still be very strong. As a result, this affects people’s health: headaches may occur, chronic diseases may worsen, and so on.

The accumulation of decommissioned odorant storage tanks is one of the most pressing problems in the country's gas distribution system.

The vast majority of gas distribution stations use the SPM odorant in their work - a mixture of lower natural mercaptans. Possessing high corrosive activity, the SPM odorant promotes the rapid accumulation of bottom sludge, consisting of corrosion products - pyrophoric iron sulfides, in metal containers for storing the odorant. In order to reduce the hazard class of decommissioned odorant storage tanks, scientists at Samara State Technical University () have developed a method for their neutralization, which makes it possible to effectively reduce the sulfur content in bottom sludge, after which the tanks can be disposed of as low-hazard waste.

In most cases, containers for storing odorant are made of materials that are not resistant to corrosion, and the disposal of waste odorant residues and failed components and vessels associated with the odorization process requires systematization and improvement.

The period of operation of working odorant storage tanks is more than 20 years. Currently, only at the Gazprom transgaz Samara enterprise there are more than 100 odorant storage tanks, with a volume from 1 m 3 to 5 m 3, taken out of service or with an expiring service life.

The purpose of this work is to develop a comprehensive environmentally and technologically safe method for recycling odorant storage containers, both recently decommissioned and those that have been mothballed for a long time.

It is known that lower mercaptans interact with iron and its oxides, forming iron mercaptides that are prone to spontaneous combustion. In addition, hydrogen sulfide in the transported gas, acting on iron and its oxides, forms corrosive deposits with pyrophoric properties, i.e. capable of spontaneous combustion even at low temperatures. These deposits consist mainly of corrosion products - iron sulfides with the general formula FexSy.

Fresh, unoxidized deposits of iron sulfide when interacting with a gas-air mixture are capable of strong heating and can be a source of explosion and fire. The main reaction leading to the most intense heating of pyrophoric deposits is the exothermic reaction of iron disulfide with atmospheric oxygen: FeS 2 + O 2 → FeS + SO 2, the thermal effect of which is 220 kJ/mol.

The rate of this heterogeneous reaction significantly depends on the conditions; it can proceed either slowly, stationary with weak heating, or with self-acceleration and intense self-heating, leading to spontaneous combustion of pyrophoric deposits. When pyrophores are heated to a temperature of 180–220 °C, spontaneous ignition of free sulfur occurs.

The slow exposure of pyrophoric deposits to oxygen leads to their gradual oxidation with the release of elemental sulfur, which fills the pores and covers the deposits with a protective film.

Iron sulfide, as is known, has a loose structure and is well wetted by water, since its surface has hydrophilic properties. In a humid environment, under the influence of oxygen, it is capable of oxidizing to iron sulfate, which is washed off from the walls of the container by condensate, dissolves in its aqueous part and accumulates at the bottom of the container, contributing to an increase in the electrical conductivity of the environment and increased metal corrosion. Thus, up to 20% of iron sulfate is found in corrosion products. The oxidation of iron sulfides can be explained according to the reaction: FeS 2 + 3.5O 2 + H 2 O → Fe 2 + +2SO 4 2- + 2H +, while hydrogen ions accumulating in the water layer give it an acidic character with a pH of within 2-4 units.

There are virtually no systematic studies in the literature devoted to the influence of a mixture of natural mercaptans (NMRs) and their transformation products on the corrosion process of steels and alloys in the presence of electrolytes.

Corrosive destruction of metals in the hydrocarbon-electrolyte system occurs much more often than is usually thought. It has been shown that two-phase condensate is more corrosive than aqueous condensate alone.

Obviously, when a metal comes into contact with a 2-phase environment, special conditions are created that sharply accelerate the corrosion process. Therefore, the study of the patterns of corrosion behavior of metals in a system of two immiscible liquids is of great practical and scientific importance.

experimental part

Analysis of odorant residue samples. A chromatographic study of the old odorant residue carried out on a Finnigan Trace DSQ GC/MS chromatography-mass spectrometer showed that about 65% of the old odorant residue consists of various dialkyl disulfides - products of oxidative intermolecular condensation of mercaptans. We analyzed samples from 11 decommissioned containers that were stored in an open area for a long time. In all samples, which are a three-phase system “odorant residue - water - corrosion products”, the ratio of mercaptans to disulfides is approximately the same, minor differences were observed only in the ratio of individual components. The formation of dialkyl disulfides is possible due to the interaction of mercaptans with active corrosion products of steel containers, as well as due to the entry of air oxygen into the containers through leaks in flange connections during long-term storage. Analysis of bottom sludge samples. One of the main objectives of this work is to study the possibility of recycling bottom sludge from used odorant storage tanks, which, as shown by the calculation method, belongs to hazard class 3 waste. In order to study this issue, a series of experiments was carried out to study the interaction of the specified sludge with ozone in an aqueous and aqueous-alkaline environment. The expected result was a sharp drop in the sulfur content in the samples. Experiments on ozonation of bottom sludge were carried out in a pilot laboratory installation. The experimental conditions and results are given in table.

1. Experimental technique. The bottom sludge sample was prepared as follows. A sample from the appropriate odorant storage container was filtered using a Schott filter, and the sludge sediment was thoroughly washed with acetone and petroleum ether and dried in air. About 4 g of a ground sample of bottom sludge was loaded into a laboratory installation and ozonated in a working solution, without stirring with a mechanical stirrer, for 4 hours at a flow rate of the ozone-air mixture of 0.5 l/min and a temperature of 23 °C. Then the precipitate was filtered off on a Schott filter, washed with distilled water and acetone, and dried in air. The elemental composition was determined by X-ray spectral fluorescence analysis (XRF), based on the dependence of the intensity of X-ray fluorescence of the chemical element being determined, excited by an X-ray tube, on its content in the sample.

The X-ray fluorescence spectrometer is calibrated using standard samples. The influence of the sample composition on the analysis results is taken into account by normalizing the line intensity of the element being determined to the intensity of the coherent scattering line of the rhodium tube radiation.

The SHIMADZU EDX-900 spectrometer used is registered in the State Register of Measuring Instruments under No. 25909-03. The sludge sample was prepared by drying at 115 °C and grinding in an agate mortar to a fraction of 200 mesh (71 µm). Two analytical samples are taken from the prepared sample, each of which is poured into a cuvette so that the layer thickness is at least 3 mm. All measurements are carried out at a tube voltage of 40 kV, a current of 100 mA using automatic background accounting and an exposure of 720 s.

Table 1. Conditions and results of experiments on ozonation of bottom sludge samples

In Fig. Figures 1 and 2 show the X-ray fluorescence spectra of samples of corrosion products before and after treatment with ozone as part of testing the developed method for neutralizing decommissioned natural gas odorant storage tanks. It should be noted that the XRF method has its limitations: for example, it is impossible to determine the content of light atoms of oxygen, nitrogen and carbon. However, the results obtained by this method give an averaged elemental composition over the entire volume of the sample.

Rice. 1a. Deposits on the inner surface of the odorant storage tank before ozonation

Rice. 1b. Deposits on the inner surface of the odorant storage tank after ozonation

Rice. 2a. Bottom sludge from the odorant storage tank before ozonation

Rice. 2b. Bottom sludge from the odorant storage tank after ozonation

Discussion of results and conclusions

The reasons for the high corrosive activity of the SPM odorant, in our opinion, lie in the presence of water impurities in its composition, although this is standardized by the relevant technical conditions for the manufacture of the odorant. Over a long service life (10 years or more), the container with odorant is repeatedly exposed to temperature changes, up to deep freezing. In this case, water dissolved in the odorant mass falls onto the walls of the container in the form of condensate and accumulates at the bottom in condensed form. With each cycle of filling the container, the amount of condensed aqueous phase increases, thus forming a highly corrosive system: odorant-electrolyte.

When a container with an expired service life is removed from service, the tightness of the flange connections is broken, through which air oxygen begins to flow freely, intensifying corrosion processes. When oxygen and active iron sulfides interact, sulfuric acid accumulates in an aqueous solution, increasing the conductivity of the electrolyte, and, consequently, the corrosion rate.

Localization of corrosion processes at the bottom of the container, against the background of their acceleration, can quickly lead to a sharp thinning of the steel bottom of the container with a residual amount of odorant under pressure and the formation of a through hole through which the remains of the odorant (a substance of the second hazard class) can fall, for example, onto the soil . It should be noted that the design of most odorant storage containers does not provide for the possibility of completely draining it. Therefore, the “residual” amount of odorant can, taking into account the volume of containers used, reach fifty or more liters. The release of such a quantity of hazardous waste onto the soil will lead to environmental damage, the economic consequences of which are easy to calculate.

Currently, a significant number of odorant storage tanks, decommissioned many years ago, create a real threat of local environmental disasters.

The environmentally friendly method of recycling storage containers and working containers of odorant developed within the framework of this work by ozonating the odorant residue and bottom sludge directly in the disposal container itself is designed to solve the problem of accumulation of this type of waste and prevent contamination of soil, water and air basins with odorant waste. Decontamination of pyrophoric deposits during ozonation will ensure the safety of further disposal of containers.

It is known that the pyrophoric properties of hydrogen sulfide corrosion products are directly related to their sulfur content.

The interaction of ozone with iron sulfide contained in bottom sludge can be represented in the form of equations:

FeS + 4O 3 → FeSO 4 + 4O 2;

2FeSO4 + O3 + 5H2O → 2Fe(OH)3 + 2H2SO4 + O2;

2Fe(OH)3 → Fe2O3 + 3H2O.

During the formation process, the iron hydroxide precipitate quickly degrades into an oxide that no longer reacts with dilute sulfuric acid, and iron ions are thus removed from solution. It is obvious that an alkaline environment in which ozone has the highest oxidative potential will facilitate the faster and more complete extraction of sulfur from corrosion products.

Based on the results of this work, the following conclusions can be drawn.

1. The remainder of the odorant in waste storage containers consists of 65% of the products of oxidative condensation of mercaptans - dialkyl disulfides. This is due to the fact that between the dismantling of the container and the beginning of measures for its disposal, a significant period of time passes, during which in the mass of the odorant residue, due to the oxidation of mercaptans by corrosion products of the container and air oxygen entering through leaks in the compounds, a significant part of the mercaptans turns into dialkyl disulfides .

2. As a result of experiments, it was shown that the reduction in sulfur content in samples of corrosion products during ozonation in a neutral environment for 4 hours is at least 2 times, and in the case of using an aqueous-alkaline solution, it exceeds 6 times. After treatment with ozone, bottom sludge completely loses its pyrophoric properties.

3. The technological solution formed after the process of ozonation of the bottom sludge of storage tanks practically does not contain dissolved iron and, by calculation method, is classified as a substance of the fourth hazard class.

Literature

1. Kovalev B.K. Some problems of gas odorization // Gazprommash Bulletin: collection. scientific-technical articles. Issue 1. URL: http://www.gazprommash.ru/factory/vestnik/vestnik1/vestnik_st6/

2. Gonik A.A. Hydrogen sulfide corrosion and measures to prevent it. M.: Nedra, 1966. 174 p.

3. AS USSR No. 1404463. IPC C01G49/12. Gadzhiev B.A., Kuliev T.M., Mehrabov M.A., Mamedov R.G., Mamedov M.F., Khalilova R.A. 1988.

4. Kekkonen F.F. Chemical control at main gas pipelines and compressor stations. L.: Nedra, 1964. 159 p.

5. Greg S., Singh K. Adsorption, specific surface area, porosity. M.: Mir, 1970. 407 p.

This material will be useful to everyone (and especially to those motorists who use propane, butane, methane). Many people are sure that the gas itself smells and when leaks occur, the smell comes from it. BUT this is often not always the case! To catch the “leakage” something needs to be added to the final composition. It is precisely because of safety that so-called “odorants” are added to almost all gaseous compounds used (which we drive). So that you and I can “catch” with our noses...

Let's start as usual with the definition

Odorants - (from the Latin ODOR - smell) - inert substances added to gas to give it a specific odor that will warn of leaks.

To put it in simple words, we catch them with our nose, and not the gaseous compounds themselves.

Requirements for odorants

Actually there are quite a lot of requirements, I will list them point by point:

• A specific smell that can be detected by the human nose
• Must be inert. Do not enter into a chemical bond with the main composition
• It must be physically harmless, that is, it must not corrode the walls of metal containers, tanks, as well as rubber and plastic hoses.
• Should not condense under any conditions, especially extreme

All this is necessary primarily in order to be effectively used in gas installations in cars. After all, the tanks there are metal, and the tubes are rubber or plastic.

Compositions and smell of odorants

Often this is a sulfur-containing compound. AT this time there are two large classes:

• Mercaptan – these are substances such as CAPTAN, CALODORANT, METHYL MERCAPTAN, ETHYL MERCAPTAN
• Sulfide – this is DIETHYLSULPHIDE, DIMETHYLSULPHIDE, DIMETHYLDISULPHIDE, TETRAHYDROTHIOPHENE

Even in the distant Soviet Union, odorants were used for natural and shale gas. At that time, technical ethyl mercaptan (C2H5SH) was widely used; it smells really sharp, I would even say disgusting - similar to rotten or rotten cabbage.

A highly mercaptan odorant, sulfan, was also used. Essentially it was waste that was generated during the cooking of kraft pulp.

Gas condensates were also collected, so in 1972 a mixture of natural mercaptans was used, which were produced in the Orenburg gas condensate field.

In the United States of America, odorants are also used, but often of petroleum origin, such as pentalarm (consisting of ethyl mercaptan, amyl mercaptan), captan (consisting mainly of a mixture of butyl mercaptans), calodorant (containing almost completely pure sulfur in sulfide or disulfide forms).

To summarize, odorants are a must! And often they have a sharply unpleasant odor that makes a person react to it!

About the smell of gas

We completely forgot about the smell of gas. There are a lot of myths that clean gas smells. However, this is not true at all! Natural gas, a fairly large amount of it, often consists of methane (CH4), a combination of carbon and hydrogen atoms. There are also small impurities of ethane (C2H6), propane (C3H8) and butane (C4H10).

What is interesting is that not only one gas in its pure form HAS NO COLOR AND ODOR! If clean gas came into our homes, it would be very difficult to “notice” it during leaks. And this is either an explosion (because they are explosive), or you can simply suffocate.

That is why almost all gases used today undergo a process of forced odorization!

Now very often, in almost all gaseous compositions, an odorant is used - ethyl mercaptan.

It is this smell that we smell at gas filling stations. And that’s all for me, I think my article was useful to you, read our AUTOBLOG.

B.K. Kovalev, deputy. General Director for R&D

PROPERTIES AND RATES FOR ADDITIVE ODORANTS

Natural gas (methane) and liquefied gases (propane-butanes) are initially odorless, so any leakage from a closed system can only be detected by special sensors. Since such gases, widely used in industrial facilities and in everyday life, in case of leakage can cause severe poisoning and, in addition, at certain concentrations create an explosive atmosphere, there is a need to quickly detect the presence of gas in the ambient air without the use of special technical devices.

For a long time, in Russia and in foreign countries, this problem has been solved by adding substances to gas that have a pronounced odor, the presence of which should indicate the presence of leaks in gas pipeline systems or gas equipment. Such substances that give gas a specific odor are called odorants, and the process of their introduction into the gas flow is called gas odorization. Odorization of natural gas is carried out, as a rule, at gas distribution stations (before supplying gas to consumers) or at centralized odorization points.

Odorants added to natural gas should ideally have the following properties:

• have a pronounced, specific smell (for clear recognition);
• exhibit physical and chemical stability in the vapor state when mixed with natural gas and moved through a pipeline (to ensure a stable dosage);
• be highly concentrated (to reduce the total consumption of the substance);
• have minimal toxicity in working concentrations and do not form toxic products during combustion (for safe operation);
• do not have a corrosive effect on the materials of gas pipelines, storage and transportation tanks, shut-off and control valves (to ensure a long service life of gas pipelines and gas equipment).

Currently, there is no odorant that fully meets the above requirements, so consumers have to put up with a number of inconveniences when working with existing odorants and strictly follow the requirements of the “Safety Instructions for the Production, Storage, Transportation (Shipment) and Use of the Odorant” - M.; OJSC Gazprom, LLC VolgoUralNIPIgaz; 1999. The wording of a number of points in this instruction causes fair criticism from specialists of operating organizations, but today there is no other official regulatory document that would complement the “Safety Rules in the Oil and Gas Industry” regarding work with odorant.

In order to take timely measures to prevent emergencies in the event of leaks, natural gas must be detected by smell when its content in the air is no more than 20% of the lower explosive limit. Based on this requirement, the odorization process must ensure such a content of odorant in the gas that a person with a normal sense of smell can detect the odor with a volume fraction of gas in the air equal to 1%. The quantitative content of odorant in the gas supplied to the consumer is standardized depending on the chemical composition of the odorization mixture used. For example, in accordance with the “Regulations on the technical operation of gas distribution stations of main gas pipelines VRD 39-1.10-069-2002”, for ethyl mercaptan the input rate is 16 g (19.1 cm³) per 1,000 m³ of gas reduced to normal conditions.

Ethyl mercaptan was one of the first industrial odorants used in the former USSR (manufacturer: Dzerzhinsky Fatty Alcohol Plant). Its main disadvantage is chemical instability, expressed in easy oxidation and the ability to interact with iron oxides (always present in gas pipelines) to form diethyl disulfide. As is known, disulfides have a significantly lower odor intensity, which reduces the performance properties of the odorant and ultimately leads to an increase in the consumption of the original substance (ethyl mercaptan). The decrease in odor intensity is especially noticeable when transporting gas odorized with ethyl mercaptan through pipelines over long distances. Other disadvantages of ethyl mercaptan include its high toxicity and solubility in water (7.5 g/l).

Since 1984, almost all GDS in Russia have used the odorant SPM (a mixture of natural mercaptans), produced according to the technical specifications TU 51-31323949-94-2002 “Natural odorant LLC Orenburggazprom” developed by VNIIGAZ. This odorant is produced at the Orenburg Gas Processing Plant from raw materials based on condensate from the Orenburg and Karachagan fields, which is unique in its composition. The SPM odorant is a multicomponent substance. According to TU 51-31323949-94-2002, its composition may contain the following mass fractions of individual mercaptans:

• ethyl mercaptan - up to 44.0%;
• iso-propyl mercaptan - up to 31.0%;
• butyl mercaptan - up to 11.0%;
• n-propyl mercaptan - up to 6.0%;
• tert-butyl mercaptan - up to 5.0%;
• n-butyl mercaptan - up to 1.5%;
• tetrohydrothiophene - up to 1.5%.

The rate of introduction of the multicomponent odorant SPM in Russia is the same as for ethyl mercaptan - 16 g (19.1 cm³) per 1,000 m³ of gas reduced to normal conditions.
In foreign countries, mercaptans obtained as a result of chemical synthesis based on sulfur, hydrogen sulfide, sulfides and other sulfur compounds are widely used as odorants. As a rule, mixtures of several substances are used, that is, a synthesized odorant, like a natural one, is a multicomponent substance. Such odorants are more stable in their chemical composition and do not contain foreign impurities. Synthesized odorants are stored and transported in vessels made of corrosion-resistant materials specially designed for these purposes.

Until recently, all manufacturers and consumers of odorization mixtures were guided by the requirements of the international standard, which recommends the use of volatile organic sulfur compounds with a boiling point below 130 ºC as an odorant. Today in Western countries the production and use of sulfur-free compounds as odorants has begun. An example is a product synthesized in Germany called Gasodor™ S-Free™, which has the following advantages:

• is an environmentally friendly product (when used, emissions of sulfur and its compounds into the atmosphere are eliminated);
• meets the requirements of sanitary and epidemiological standards;
• has a sharp signaling odor;
• provides the required odor intensity at lower concentrations compared to odorants based on sulfur compounds;
• has high stability (including during storage);
• does not change technical, chemical and odorant properties during sudden temperature fluctuations;
• practically insoluble in water and liquid hydrocarbons.

The Gasodor™ S-Free™ odorant passed operational tests in November 2004 at one of the facilities of Severgazprom LLC and was found suitable for use at the facilities of OJSC Gazprom (the operational test report was approved on December 12, 2004 by the head of the Department for Transportation, Underground storage and use of gas, B.V. Budzulyak). During the tests, the odorant concentration was 10-12 mg/m³, and the existing odorization equipment of the existing gas distribution station was used.

The draft “Temporary technical requirements for gas distribution stations”, currently sent for consideration to organizations of OJSC Gazprom, provides for the odorization of gas, along with SPM, the use of the Gasodor™ S-Free™ odorant, as well as crotonaldehyde.

Crotonaldehyde according to TU 2417-080-00203766-2003 is a transparent (from light yellow to light brown), flammable liquid with a pungent odor. According to the degree of impact on the human body, this substance belongs to the second hazard class (GOST 12.1.007). Unfortunately, there is not enough information in the public press about the use of crotonaldehyde as an odorant, indicating its performance characteristics.

Recently, reasoned proposals to abolish strictly regulated norms for introducing odorant into the gas flow have been increasingly voiced. When establishing an individual standard for each facility, it is proposed to take into account the condition and length of the gas pipeline, the chemical composition and quality of the transported gas, the quality and component composition of the odorant used, as well as the method and accuracy of gas odorization. Let's consider how the factors listed above affect the quality of gas odorization.

Condition and length of the gas pipeline. As noted above, ethyl mercaptan, which is one of the main components of the SPM odorant, enters into a chemical reaction with iron oxides formed on the walls of the gas pipeline due to corrosion. As a result of this interaction, the intensity of the odor of the odorized gas decreases and, as a result, an increase in the rate of introduction of the odorant into the gas flow is required.

Unfortunately, official sources of information do not contain information on this issue for gas pipelines based on polyethylene pipes.

Chemical composition and quality of transported gas. It is generally accepted that the main factor in the odor quality of an odorization mixture is the proportion of mercaptan sulfur in it. Knowing the percentage of mercaptan sulfur in the transported gas, it is possible to reduce the rate of introduction of odorant into the gas flow.

At the same time, poor quality of gas, the presence of impurities in it - in particular, increased moisture content, can lead, under appropriate conditions, to the accumulation of condensate in the gas pipeline and to the subsequent dissolution of part of the odorant in these hydrocarbons, with an inevitable weakening of the intensity of the gas odor for the consumer. In such cases, it will be necessary to increase the rate of odorant introduction into the gas flow.

The quality and component composition of the odorant used. Unfortunately, the conditions for transportation and storage of odorant in Russia leave much to be desired. Often for these purposes, black steel containers are used, which are subject to the aggressive effects of odorant. In some cases, storage and transportation of containers with odorant are carried out under conditions of sudden temperature changes and various atmospheric precipitations. Reusing containers made of black steel will obviously degrade the quality of the odorant poured into them. Various sources unanimously testify: during transportation, the quality of the odorant deteriorates significantly.

As for the component composition of the odorant, some competent specialists note quite significant fluctuations in the ratio of the various components of the SPM odorant produced by the Orenburg GPP, and even the presence of methyl mercaptan in its composition, which according to TU 51-31323949-94-2002 should not be present. In addition, a significant decrease in the mass fraction of such important components as ethyl mercaptan and tert-butyl mercaptan was revealed. Such changes are associated with the instability of the composition of the condensate used as a raw material and can negatively affect the intensity of the odor of the odorized gas if the rate of introduction of the odorant into the gas flow is not changed.

At the same time, analysis of the component composition of an odorant in natural gas is still a complex and expensive procedure that does not have proven methods for practical use. Automation of the gas odorization process based on such analysis will not only allow optimizing odorant consumption, but also move to a fundamentally new level in addressing safety and environmental issues. Work in this direction is underway, but its practical implementation is still ahead.

Method and accuracy of gas odorization. Along with other factors, the quality of gas odorization directly depends on the odorization method and the accuracy of odorization provided by this method, as well as, to a large extent, on the degree of automation and elemental base of the equipment that implements the gas odorization process with simultaneous analysis of the results of this process. Taking into account the continuous dynamics in the improvement of technologies and equipment, we should expect in the near future the emergence of fundamentally new technical solutions in this area that will make it possible to quickly change the dosage of the odorant introduced into the gas flow, based on an express analysis of the component composition of the odorization mixture. In this case, it will inevitably be necessary to introduce appropriate changes to all regulatory and technical documents affecting the processes of production, storage, transportation and use of the odorant.

So, an analysis of the factors influencing the quality of odorization shows that in the future, with appropriate software and hardware support for the odorization process, the rate of introduction of odorant into the gas flow may become a variable value. Moreover, there are two possible options for varying the numerical value of this norm.

Option 1. Using a specially developed methodology, for each specific object, taking into account all the above factors, an individual numerical value of the norm for introducing odorant into the gas flow is calculated and entered into the gas odorization control system. Subsequently, the control system monitors the fulfillment of the specified norm value.

Option 2. The numerical value of the rate of odorant input into the gas flow is entered into the gas odorization control system in average form (for the actually used odorant), and is subsequently periodically adjusted by the control system based on the results of continuous processing of the feedback signal coming from an intelligent device for monitoring the quality of odorized gas.

It should be noted that the first option involves working with an odorant that has a stable composition and is more suitable for chemically synthesized odorants, although with some degree of error it can also be used for the SPM odorant. If an approved methodology is available, this option can be implemented on the basis of existing ODDK gas odorizers produced by the Gazprommash plant (Saratov).

The second option is more universal, but its implementation requires a reliable intelligent device for monitoring the quality of odorized gas, which must have an acceptable price for mass use. Currently, specialists from the R&D departments of the Gazprommash plant are working to create such a device based on modern technologies. In combination with a new device, the ODDC gas odorizer can ensure the implementation of the second option without additional work on site, with the exception of installation and connection of the device itself.

Since the raw material base for the production of natural odorant is far from exhausted, and work to improve the quality of SPM at the Orenburg gas processing plant continues, we can expect that the use of domestic odorant at Russian gas processing plants will continue for a long time. Consequently, the introduction of modern gas odorization technologies using the ODDC gas odorizer, which allows working with various odorants without radical reconstruction of the facility, is very important today.

ODORIZATION UNITS GRS

The quality of gas odorization is largely determined by the odorization method and the equipment that carries out the odorization process. The choice of odorization method and type of gas odorizer depends on the required performance, required accuracy and material capabilities of the customer.

The odorant can be introduced into the gas stream, both in liquid and vapor state. In the liquid state, the odorant is supplied to the gas pipeline using a dropper or a dosing pump. To odorize with odorant vapors, part of the general gas flow branches off, is saturated with odorant vapors, moving over the liquid odorant, bubbling through it, or blowing on a wick wetted in the odorant, and returns to the general gas flow.

Drip method of introducing odorant into a gas flow. This method, due to its simplicity and low cost, despite the increased requirements for the quality of gas odorization, remains the most common at existing Russian gas distribution stations. It is based on a relatively constant value of the mass of one drop of liquid (for an odorant, the mass of one drop is considered equal to 0.02 g, that is, 1 g of odorant contains approximately 50 drops). By adjusting the supply of odorant and counting the number of drops per unit time, it is possible to achieve the required odorant flow rate for the set gas flow rate. At high gas flow rates, a sequence of odorant drops is transformed into a stream of liquid. In this case, the consumption of the odorant is monitored using the scale of the level gauge of the supply tank (on some gas odorizers, a special measuring tank is installed for this purpose, with a pre-verified division value).

This method requires constant checking and adjustment of the odorant flow through the dropper when gas flow changes (for example, when connecting or disconnecting individual consumers). Such adjustments are performed manually by the GDS operator and cannot be automated. The actual accuracy of odorization is low (ranges from 10 to 25%). Therefore, in modern odorization installations, the dropper is used only as a reserve for operation during the repair of main equipment.

Wick odorizer, as a rule, it is used for small, slightly varying gas flow rates using an odorant that is stable in chemical composition (both for liquid and vapor). The odorant content in the odorized gas is estimated by the amount of odorant consumed per unit time and can be regulated by changing the amount of gas passed through the wick. The regulation is carried out manually by the GDS operator and high accuracy of odorization, however, cannot be achieved.

Bubbler method of introducing odorant into a gas flow. Unlike a dripper and wick odorizer, odorization plants using bubbling can already be automated. Examples are OD gas odorizers, shown in Figure 1 (manufacturer - Gazprommash Plant LLC) and BO odorization units (manufacturer - Saratovgazpriboravtomatika LLC).

Figure 1. OD gas odorizer

In these devices, automatic supply of odorant, proportional to the flow rate of the odorized gas, is ensured using a diaphragm installed in the pipeline and a special dispenser. When a gas flow moves through a pipeline, a pressure drop occurs across the diaphragm, the value of which changes in proportion to the flow rate of the moving gas. Part of the gas flow branches off and enters the dispenser through a control valve, where, bubbling through the liquid odorant, it is saturated with its vapor. Next, the gas saturated with odorant vapors passes through the viewing window, returns to the pipeline on the other side of the diaphragm and mixes with the main gas flow. The odorant is continuously fed into the dispenser by gravity from the supply container. The supply container is replenished periodically by pressing from the reserve container for storing odorant. All refills are carried out in a closed manner using an ejector, which ensures the removal of odorant vapors from the containers and from the hose of the tanker truck with subsequent discharge of these vapors into the pipeline. It should be noted that the use of an ejector is effective only if the ratio of its input pressure (taken at the inlet of the gas distribution system) to the output pressure is from 2 to 3. In other cases, to neutralize odorant vapors, a deodorizer with a filling of 50-70% should be used its volume with a neutralizer (for example, a 20% bleach solution).

The presence of odorant in the supply container is monitored visually by the GDS operator. In addition, provision is made for transmitting a warning signal about the minimum level of odorant in the supply tank to the GDS control system.

Odorization plants of the OD and BO types have a number of significant disadvantages that limit the widespread use of these devices. These include the following:

• if gas consumption changes during the operation of the odorizer by more than 30%, the odorization process exits the mode and requires manual adjustment to a new mode;
• odorization accuracy is low (depending on operating conditions, it can vary from 5 to 20%), and it is determined only by the quality of the dispenser and the stability of gas flow in the pipeline; temperature fluctuations in the ambient air, as well as sudden changes in gas consumption in the form of shutdowns or connections of relatively large gas consumers, significantly worsen the quality of odorization, but cannot be automatically taken into account and compensated for in these devices;
• the need to use a restriction device creates additional inconvenience for maintenance personnel, and often requires seasonal replacement of the washer;
• Only warning information about the minimum level of odorant in the supply tank is transmitted to the GDS control system or to upper-level systems; There are no other sensors for assessing the condition of the odorizer equipment and the quality of its operation.

Metered supply of odorant into the gas flow. There are different ways to implement dosed introduction of odorant into the gas flow.

Initially, dosing the odorant supply was reduced to installing an electromagnetic valve in front of the dropper, controlled from an electronic unit, which provided a specified time for the valve to be open, as well as the frequency of its activation. Thus, a unit dose was determined by the amount of odorant passed through the solenoid valve while it was in the open state, and the required rate of odorant introduction into the gas flow was ensured by selecting the desired frequency of valve activation. Unlike previous methods, dosing the odorant using an electromagnetic valve allows you to improve the quality of odorization, and if you have the appropriate software and hardware, organize automatic supply of odorant in proportion to gas flow and indirect accounting of the introduced odorant (by the number of times the solenoid valve is activated). At the same time, this method is not widely used due to a number of significant disadvantages:

• in case of leaks through the valve, the gas odorization process becomes uncontrollable, since the odorant is supplied to the pipeline by gravity
• the value of a single dose largely depends on the ambient temperature (due to temperature changes in volume, the density of the substance changes and, as a consequence, the mass of the dose) and on the degree of filling of the supply container (with a change in hydrostatic pressure, the supply rate of the odorant changes and, accordingly, its quantity flowing through an open solenoid valve at the same time);
• there is no information about the actual passage of the odorant through the odorizer (there is only visual control).

Subsequently, metering pumps were used for dosed supply of odorant, which made it possible to significantly improve the process of gas odorization. As a rule, odorant dispensers are made on the basis of such pumps, which contain, in addition to the pump itself, a filter for cleaning the odorant, a control device (depending on the design of the dispenser, this can be an electromagnet or an electro-pneumatic valve) and an electronic control unit.

Odorant dispenser DO1-25. Developed and manufactured by Samara aviators, the odorant dispenser is a plunger pump with an adjustable piston stroke, controlled by an electric pneumatic valve from an electronic unit. The dose (from 1 to 25 cm³) is set by setting the piston stroke limiter to the desired position along the dial on the adjusting head. The electronic control unit provides the required operating frequency of the control valve, set by the operator based on the current gas flow. The piston moves using gas from a high pressure gas pipeline. In this case, the pressure difference between the gas pipelines of the high and low sides must be at least 0.6 MPa. The incoming odorant passes through a filter before entering the pump.

These dispensers are used mainly at the facilities of Samaratransgaz LLC. Their disadvantages include a complicated design and the presence of a large number of sealing elements, which are potential sources of leaks.

Automated gas odorization system (AGOS). ASOG, created by nuclear scientists from Sarov, is essentially an odorant dispenser, but unlike DO1-25, with a higher degree of automation. In addition, here we are dealing with microdoses (0.15-0.45 cm³), which increases the requirements for the purity of the odorant (any solid particles that get into the needle valve disrupt the normal operation of the dispenser). ASOG has a fine filter, as well as a new element - an odorant supply sensor, which already allows you to have information about the odorant actually entering the pipeline. Unfortunately, operating organizations note the low reliability of this sensor. The ASOG control unit is connected to a standard flow meter of the odorized gas and ensures the supply of odorant into the pipeline in proportion to the gas flow with an accuracy of no worse than 5%.

The Gazprommash plant developed and manufactured on the basis of ASOG Gas odorizer with metered gas supply (ODD) for the northern regions. The ODD odorizer is located in an insulated block box with heating, lighting, gas control and forced-air supply and exhaust systems. In addition to ASOG, the odorizer is equipped with a 110-liter supply tank, a deodorizer, a reserve dropper and the necessary shut-off valves. At the customer's request, the ODD is equipped with an ejector for closed filling of containers. As a reserve capacity for storing odorant, a container for transporting odorant with a volume of 1.5 m³ is used, installed next to the block box. The ODD odorizer is successfully operated at the gas distribution station of Surgutneftegaz OJSC in Surgut. A similar odorizer produced by the Gazprommash plant, but located not in a block box, but in a cabinet, operates at one of the facilities of Permtransgaz LLC (Figure 2).

Figure 2. ODD gas odorizer based on ASOG

Due to the complicated design of the dispenser and the presence of small gaps in the valve groups, ASOG is often “capricious” when working with domestic odorant, so the demand for odorants using this system is low.

Electronically controlled odorization unit (ECU). Odorization units of the BOE type, manufactured by Saratovgazpriboravtomatika LLC, are complete devices for gas odorization, providing dosed injection of odorant in proportion to gas flow and capable of transmitting a generalized alarm signal to the facility’s process control system. BOEs are equipped with a supply tank of the required volume and a restriction device of the appropriate standard size, as well as a dosing pump of the required capacity. In addition, the piping of the odorization unit includes a reserve dropper, an ejector and shut-off valves.

Dosed injection of odorant is carried out by a membrane pump with a pneumatic drive, which is controlled by an electromagnetic valve. Calculation of the flow rate of odorized gas and generation of control signals is performed by a microprocessor control unit. The pre-required dose is set on the pump using a special controller.

BOE odorization units are a development of BO type odorization units previously produced by Saratovgazpriboravtomatika and automatically inherited some of their shortcomings, for example, the presence of a restriction device. In addition to the fact that this device creates certain inconveniences and additional problems during maintenance, the calculation of gas consumption performed by the control unit often differs significantly from the readings of a standard flow meter, and this can lead to unacceptable odorization errors (in particular, the gas temperature is not taken into account).

Gas odorizer with dosed supply of odorant and automatic correction of the degree of odorization based on both current gas consumption and real odorant consumption (RODC). Gas odorizers ODDC, mass-produced by the Gazprommash plant since April 2007, represent a new generation of odorization units that allow solving complex problems of creating automated systems focused on centralized forms of service and unmanned technologies.

An analysis of the capabilities of existing odorant dispensers and odorization installations showed that the desire to ensure high dosing accuracy ultimately leads to a more complex design of the dosing device. In turn, the complication of the design replaces the solved problems with new ones, forcing further complications. Specialists from the Gazprommash plant solved the problem of increasing the accuracy of odorization in their own way. The ODDC gas odorizer can use any dosing pump that provides the performance required by the consumer. High accuracy of odorization (according to the passport - no worse than 2%) is achieved by constantly taking into account the odorant actually passing through the pump and timely adjustment of the signal that controls the operation of the pump. In this case, the value of the current gas consumption taken from the standard flow meter is taken into account. The odorant is accounted for using the hydrostatic method in mass units, which eliminates the influence of temperature fluctuations and associated changes in the volume of the substance. The odorizer control unit can work with any types of signals from flow-measuring systems specified when ordering the odorizer, and can also be integrated with any upper-level systems. The main exchange protocol is MODBUS; information exchange is possible using any other agreed protocol.

The main design of such an odorizer is considered to be ODDC 02 (Figures 3, 4).

Figure 3.
Gas odorizer ODDK 02

Figure 4.
Layout of gas odorizer ODDK 02

In this option, all equipment is placed in an insulated cabinet with lighting, electrical heating, and natural ventilation systems. The odorizer includes: a 110 liter consumable container. made of stainless steel, an ejector, a self-made metering pump, a pressure difference sensor, an inspection window, a reserve dropper, shut-off valves and piping elements (Hamlet or Swagelok). ODDK 02 is equipped with a control unit BUO - Figure 5 (for installation in control and instrumentation units) and a deodorizer.

Odorizer ODDC 01 (Figure 6) is designed for installation in addition to the existing dropper from the existing supply tank. The equipment of such an odorizer is located in a cold cabinet and does not contain a supply container, ejector, or dropper.

Figure 5.
Gas odorizer ODDK 01

Figure 6.
Control unit BUO

The equipment of the ODDC 03 odorizer is located in a block box.

Imported odorization units. Recently, foreign manufacturers of odorization units have been increasingly knocking on the Russian gas equipment market. Imported odorizers and individual components of odorization plants are used at a number of gas distribution stations in Russia. However, their wider distribution in Russian territories is hampered by the following factors:

• high cost of foreign equipment;
• composition and quality of domestic odorant.

Considering the fact that the entire Russian economy is going through a very difficult period, foreign manufacturers have filled our country with consumer goods at relatively affordable prices. In industry, especially in its strategic sectors, such availability cannot be expected. Therefore, the creation of domestic gas equipment of a modern level seems more promising. Contacts with gas equipment manufacturers in Germany (RMG) and Italy (Tartarini) show that the price scale set for Russia in the West will not change significantly in the near future. Products from the Czech Republic and Serbia are somewhat more attractive in price; moreover, the equipment of these countries is more adapted to Russian climatic conditions. Well-known Ukrainian gas equipment cannot yet compete with the best Russian models.

Experience with foreign equipment indicates the need for significant refinement for operation in Russian conditions. For example, a gas odorizer assembled from German components from RMG (Figure 7) according to a German technological scheme turned out to be completely unsuitable for work in our climate zone using the natural domestic odorant SPM. Also, the German system of uninterrupted supply of odorant to gas distribution stations, based on the timely delivery and replacement of 50-liter containers with odorant, cannot be implemented in Russian territories.

Figure 7. Dosing pump for RMG odorant

At the same time, the rich experience of foreign gas equipment specialists deserves the most careful study and application, to one degree or another, in the development and manufacture of odorization equipment for Russian facilities.

AUTOMATED GAS ODORIZATION SYSTEMS

Recently, thanks to significant progress in the field of computer science and electronics, the automation of technological facilities has been experiencing a rapid rise. Modern electronic equipment components make it possible to create compact, highly reliable automatic control systems and intelligent sensors. The process of manufacturing the hardware of such systems has also been simplified and often comes down to “screwdriver technology.” The following tasks have come to the fore:

• development and optimization of control algorithms, including a full range of information, computing, control and diagnostic tasks;
• selection of the optimal option from the variety of offered hardware and technical means, taking into account the complexity of the tasks being solved and the financial capabilities of the Customer;
• selection of reliable actuators and mechanisms, with the ability to control from a designed controller or control complex;
• development of software that implements all tasks reflected by the control algorithm;
• ensuring the possibility of integration into top-level systems and the implementation of information exchange between these systems using a standard protocol or special, pre-agreed exchange protocols.

As a result of solving these problems, a specialized system for automatic control of technological equipment of a given facility appears.

In relation to gas distribution stations, such systems are created taking into account the established form of service. A centralized form of servicing gas distribution stations requires a higher level of automation of process equipment, and often an obstacle to the transition to this form is the process of gas odorization, since servicing most existing odorization plants is impossible without the daily presence of a gas distribution station operator. Therefore, an automated gas odorization system should be based on a reliable, modern gas odorizer with an individual control system, providing not only gas odorization, but also accounting for the consumed odorant, automatic refilling of the consumable container, and transmission of detailed information about the state of the odorization unit to the control center (including technological parameters and amount of odorant available). Separate elements of such an automated system are available at a number of gas distribution stations in Russia. However, the task of creating a complete system has not yet been fully solved. This circumstance is due to the lack of reliable and durable components capable of operating in a natural odorant environment (solenoid valves of various sizes, serial level sensors, vessels made of corrosion-resistant materials, etc.). There is clearly not enough work being done to create domestic products for completing odorization installations, so the organizations and individual specialists performing them deserve special support. The result of such work was, for example, the following products.

Electromagnetic valves for working with odorant. In the process of creating the ODDC gas odorizer, the Gazprommash plant took part in financing the work of NPP Technoproekt (Penza) to develop explosion-proof electromagnetic valves for the odorant. The valves were tested as part of a prototype of the gas odorizer ODDC 01 at the Penza LPU MG and are successfully used for mass production of the entire range of odorizers of this type.

Double-walled container for storing odorant. For uninterrupted operation of the gas distribution system, there must always be a reserve supply of odorant at its site. The most common way to create such a reserve is to store the required amount of odorant in underground containers. It should be noted that the storage conditions of the odorant, as a rule, do not meet modern requirements. In most cases, odorant storage containers are made of non-corrosion resistant materials. Often these containers do not have alarms or level indicators; inspection of their condition is practically not carried out, as it is associated with a number of organizational and technical difficulties, and the disposal of waste and failed components and vessels associated with the odorization process still does not have a regulatory framework.

The development by specialists of JSC NIIPTKHIMMASH (Penza) of double-walled containers for storing odorant significantly contributes to solving the problem of proper storage of odorant and controlling its consumption. The design of such a container ensures constant control of the space between the walls and prevents the possibility of contamination of the soil, as well as atmospheric air, in the event of a violation of the seal of the housing. The main (internal) container is made of stainless steel, which significantly reduces the degree of contamination of the odorant stored in it with corrosion products. The level indicator allows you to issue a warning signal about the need to replenish odorant reserves.

Pumps for pumping odorant. In most cases, filling the supply container of an odorization unit is carried out using the squeezing method. It is sometimes more convenient to automate this process using a pump. Such pumps, capable of pumping odorants, including into pressure vessels, are produced by Neftemash OJSC - Sapkon (Saratov). At the customer's request, pumping units can be equipped with filters.

Intelligent level sensor. Specialists from the Gazprommash plant (Saratov) have developed a sensor for measuring the level of odorant in a closed container under pressure (Figure 8). The operation of the sensor is based on the hydrostatic method, which allows, directly in the microprocessor control unit, to calculate the level, volume and mass of the liquid with high accuracy. Currently, the design is being finalized and the software and mathematics of the smart sensor are being tested for the real conditions of a gas distribution station.

Figure 8. Smart Level Sensor

The products discussed above, along with the well-known equipment for gas odorization, should help in solving the problem of creating a comprehensive automated gas odorization system. A serious step in identifying problems in this area was taken by specialists from the Penza MGP health facility, Volgotransgaz LLC, who proposed organizing such work at one of their facilities.

In December 2006 OJSC VNIIGAZ (Moscow) held a meeting on the issue of using underground double-walled tanks for storing odorant, developed by specialists from OJSC NIIPTKHIMMASH. The meeting was attended by representatives of the Office for the Transportation of Gas and Gas Condensate of OJSC Gazprom, DOJSC Orgenergogaz, LLC Volgotransgaz, OJSC Giprogaztsentr, LLC Gaznadzor, FSUE PO Start, OJSC NIIPTHIMMASH, LLC Gazprommash Plant " Continuing the main topic of the conversation, the concept prepared by specialists from Volgotransgaz LLC (together with other meeting participants) was considered to create, based on the ODDK gas odorizer of the Gazprommash plant, with a modern microprocessor control unit of an automated gas odorization system for a comprehensive solution to all problems associated with this process , including recycling of production waste. Unfortunately, the meeting did not resolve organizational issues on this issue, but the relevance of the identified task was unanimously noted.

It must also be said that recently problems associated with gas odorization have attracted the attention of representatives of various sectors of Russian industry, and some results of this interest are already noticeable. For the first time in many years, competition arose in the odorization equipment market. This circumstance, combined with obvious progress in the creation of software and hardware automation tools and smart sensors, allows us to look into the future with optimism and prepare for a very early modernization of outdated odorization equipment at Russian gas distribution stations.