Industrial uses of natural gas
Uses of natural gas in industrial activities
Industry accounts for approximately 17% of final energy consumption in France. Natural gas represents more than 40% of energy consumption in the industry, mainly in the following sectors : chemical, agri-food, metallurgy, cardboard, glass, ceramics (tiles and bricks, porcelain)…
The benefits of natural gas are numerous for manufacturers:
Security of supply: The gas is delivered to industrial sites by underground pipes, well protected from the vagaries of the weather. It arrives on the French territory from many producing countries, by LNG carriers (in liquefied form) or by gas pipelines. It is even starting to be produced on the French territory from waste from agriculture or agri-food industries (biomethane). It is stored in underground reservoirs during summer to cover major needs in winter and during peaks.
Ease of use: The installations can be easily automated, and their start-up is simple and quick. As the gas arrives under pressure, it easily supplies all of the site's facilities. The maintenance of the installations is reduced, with no need for sweeping.
Wide variety of uses: Natural gas can supply installations from a few kW to several tens of MW, operating from 20°C to 1600°C, to cook, melt, heat, cut, clean up, dry, dehydrate, sterilize, produce electricity, hot water, steam, hot air, etc.
Energy efficiency: Its combustion generates almost no pollutants, heat recovery from the fumes can be optimized to achieve returns above 95% with moderate investments.
The paper industry
This industry includes several sectors: packaging paper, cardboard, graphic paper, household and sanitary paper… for which the manufacturing process is always substantially the same.
Paper pulp is either produced on site from recycled wood or paper or purchased from specialized pulp mills.
This paste, essentially made up of cellulose fiber, is placed in a liquid solution in order to be able to homogenize it.
Papermaking consists of making the sheet and drying it.
The paste is first deposited in a thin layer on a pierced cloth on which it drips, then the sheet being formed passes between 2 cylinders which press it to extract water by mechanical energy. The sheet then passes through the drying section of the paper machine. This part generally consists of a set of drying cylinders (heated internally by steam). Drying is optionally completed by means of hot air or infrared.
Note: in this industry, the uses of natural gas are concentrated in this drying area (production of steam, hot air or infrared) which represents ¾ of the site's gas consumption.
Once dried, the sheet of paper passes through the finishing section (calender) to give it its final appearance (gloss, satin, etc.) then it is cut and rolled up on a reel.
The glass industry
This industry includes several sectors: flat glass, hollow glass, fiberglass, special glasses, crystal… for which the manufacturing process is always substantially the same, at least for the glass production part. Differences appear depending on the type of product manufactured: glass plate, bottles and jars, flasks, fibres, etc.
Glass is made up of abundant and natural raw materials, mainly sand as well as products added to reduce the melting temperature and some additives (colouring, etc.). To produce crystal, lead must be added to these ingredients
To this mixture is added cullet, broken glass from manufacturing waste, selective waste collection. The use of cullet enables waste recovery as well as energy and raw material savings.
The manufacture of glass consists of melting these products by bringing them to a very high temperature and then shaping them during controlled cooling.
These raw materials are introduced into the melting furnace. Depending on the type of glass, the temperature in the oven varies from 1300 to 1500°C.
Usually, fusion energy is provided by natural gas. An electrical or heavy fuel oil supplement is sometimes used in specific cases (dark glass, etc.). The melting furnace represents approximately 80% of the energy consumed in a glass factory.
The molten glass then passes through refining and homogenization zones always maintained at high temperature by natural gas burners and then, after shaping, into annealing tunnels also called arches to eliminate the points of tension which can be appeared during cooling. In these tunnels, the glass object is raised to a temperature of approximately 400-600°C, before slowly cooling.
The tile and brick industry
The main material used in the composition of tiles and bricks is clay, which is why the factories are located in the immediate vicinity of the quarries.
The clay, once extracted, is crushed and mixed in order to obtain a homogeneous material. This powder is then moistened so that it can be shaped by pressing or extrusion to produce tiles or bricks of various shapes. These parts can optionally be covered with mineral pigments to give them a specific color.
They are then dried (generally between 24 to 48 hours) at a controlled temperature and humidity to prevent them from cracking.
The dry products are stacked on wagons which move progressively through the gas-heated tunnel kiln to be cooked there. In this oven, which can exceed a hundred meters in length, the temperature gradually rises to a level that can reach 1100°C. The complete duration of the cooking can be around twenty hours.
The fired pieces are gradually cooled (still in the oven) then checked before being packed on pallets for shipment.
The chemical industry is an industrial sector that manufactures different products using multiple chemical reactions. It includes petrochemicals, the manufacture of polymers, the manufacture of drugs, etc.
Depending on the product manufactured, the process followed will be very different but the principles always remain the same.
The reagents (sometimes natural gas) introduced into the reactors are first purified in order to remove all the undesirable molecules. This is usually done using catalysts under well-defined temperature and pressure conditions.
Heating can be done in ovens, by means of steam-heated exchangers….
Reactions take place either continuously or discontinuously in reactors. Temperature control is often essential because it determines the balance of reactions and the products produced. Often, in batch reactors, the mixture is suddenly cooled in order to “freeze” the composition obtained.
In order to separate the products obtained, distillation operations can be undertaken (heating and cooling).
Some products need to be dried. This operation is carried out using heated air in different types of dryers (spray tower, tunnel dryer, drying tower, etc.) depending on the state of the product: liquid or solid.
The agri-food industry : the sugar
The agri-food industry is made up of many sub-sectors, with three major sectors: sugar, milk and starch products (starch of different origins) which alone 3 represent 59% of the 30 TWh of gas consumed in this sector. The other parts of the food industry are more fragmented (bakeries, biscuit factories, animal foods, alcohols and spirits, slaughterhouses, etc.).
The focus is on the production of sugar from sugar beet in mainland France. You should know that the greatest production of sugar is from sugar cane. The stages are similar in both cases with the exception of the initial stage which is done by grinding for the cane and by diffusion for the beet.
These sites operate seasonally. The start of the campaign depends on the production yield of the beets and their arrival at maturity. Generally it extends from mid-September to mid-January.
The main heat-consuming steps are the heating of liquids, drying and concentration-evaporation. The energy carrier used is steam. Thus 85% of the energy used in a sugar factory comes from the boilers for these different stages.
The consumption of natural gas in the boiler represents approximately 50% of total consumption in industry (excluding electricity production and raw materials).
Boilers are present in almost all sectors of activity, as soon as there is a need for steam or hot water: stationery, chemicals, pharmaceuticals, food processing, textiles, laundry, electricity production, etc.
Depending on the sector, the heat transfer fluid may be different (water, steam, thermal oil) and therefore the boiler as well.
A boiler is a device that continuously produces hot water, steam, superheated water, or modifies the temperature of a thermal fluid using the heat released by combustion.
There are 3 families of boilers: fire tube boilers, the most common, water tube boilers and coil boilers.
Boilers with smoke tubes: This is the boiler most frequently used by manufacturers. The fumes leaving the combustion chamber pass through tubes immersed in water before leaving the boiler to be extracted through the chimney.
This type of boiler can equally well produce steam (up to 25 bar) or hot water.
Its power range is very wide: from 1 to 35 MW and its performance is remarkable, efficiency can reach almost 100% (on PCI) or even more by adding heat recovery (economizer and condenser)
Boilers with water tubes: This is a boiler frequently used by manufacturers. The combustion chamber is covered with tubes through which the water circulates.
This design makes it possible to manufacture installations capable of reaching very high pressures (up to 170 bar) as well as high powers of nearly 300 MW.
Due to their dimensions, these boilers are generally heated by several burners.
The efficiency of such equipment is slightly lower than that of previous boilers, while being around 95%
Coil boilers: These boilers are rarer and used for specific needs:
High temperature of nearly 300°C without high pressure using thermal oil,
Need for steam with large load variations.
These are generally low-power generators (less than 10 MW) but capable of reaching pressures of up to 100 bar.
The standard efficiency of this type of equipment is approximately 90% and can reach 95% with the addition of an economizer (heat recovery unit installed on the flue gases just before the chimney).
Cogeneration is the simultaneous production of heat and electrical energy. The most common case is production by heat engines or gas turbines.
The principle is as follows: the fumes from the combustion of the gas are used to turn the alternator which produces the electricity. Then these fumes, using an exchanger, produce hot water which can be used for heating buildings or for the industrial process.
Cogeneration has an undeniable advantage: it consumes 15% to 30% less energy than the best available techniques taken separately to produce the same quantities of heat and electricity: a gas condensing boiler for hot water and a combined cycle gas plant for electricity.
These installations are found on sites that have heat needs (hot water or steam) all year round: paper mills, greenhouse growers, chemicals, dairy...
The principle of these engines is the same as the one of our cars. The gas is used as fuel. The combustion of gas in the cylinders turns the crankshaft driving the alternator which produces electricity.
Heat recovery takes place at 2 levels (almost equally): on the one hand on the engine cooling circuit (temperature of approximately 90-95°C) and on the other hand on the fumes ( temperature around 450°C). This heat is used to produce hot water or even steam.
For a consumption of 100 kW, a motor provides between 35 and 45 kWe of electricity and between 45 and 55 kWth of heat, ie an overall efficiency close to 90%.
Gas engines have electrical powers from a hundred kW to almost 5 MW.
The principle of these engines is the same as that of aircraft jet engines.
A gas turbine is made up of 3 successive parts: first of all a rotary compressor which sucks in the air and compresses it, then the combustion chamber in which the gas is injected and burnt and finally the actual turbine which is put in rotation by the hot and pressurized gases resulting from the combustion.
The mechanical energy provided by the turbine rotates the shaft driving the air compressor and the alternator producing electricity.
Hot exhaust gases (over 500°C) are typically used to produce steam in a waste heat boiler.
For a consumption of 100 kW, a turbine provides between 30 and 35 kWe of electricity and between 50 and 60 kWth of heat, ie an overall efficiency close to 90%.
Gas turbines have electrical powers from a few MW to almost 600 MW. Those encountered in cogeneration on industrial sites generally have a power of between 5 and 100 MWe.