Main Emissions of solid fuel boilers Altep About emissions from solid fuel boilers

Про викиди твердопаливних котлів

It is known that any solid fuel boiler provides heat to the room through the combustion of fuel, while generating carbon monoxide and other harmful substances.

Most modern boilers are equipped with an automatic fuel supply (including household appliances). In addition, they usually have a better system for regulating the combustion process, compared to boilers with manual fuel supply. They usually require fuel of standard and consistent quality.

In Europe, solid biofuels based on plant biomass (mainly wood) are increasingly displacing fossil fuels (oil, coal, gas) from the heat market every year. Thus, measures are being taken to protect the environment by reducing greenhouse gas and dust emissions into the atmosphere.

Emissions caused by incomplete combustion are mainly the result of insufficient mixing of combustion air and fuel in the combustion chamber, a general lack of available oxygen, too low a temperature, short residence time and too high a concentration.

As a result of incomplete combustion in boilers, the following components can be released into the atmosphere: carbon monoxide (CO), particulate matter (PM) and non-methane volatile organic compounds (NMVOCs), ammonia (), polycyclic aromatic hydrocarbons (PAHs), as well as polychlorinated dibenzoparadioxins and furans (PCDD/Fs).

 A small amount of ammonia can be released as a result of the incomplete combustion of all nitrogen-containing solid fuels. This occurs in cases where the combustion temperature is very low (fireplaces, stoves, boilers of old design).

In most cases, emissions can be reduced by basic measures aimed at reducing incomplete combustion products and improving efficiency.

The total amount of suspended particulate matter - particulate matter in the flue gases that are formed as a result of fuel combustion (in particular, solid mineral fuels and biomass) can be defined as carbon, smoke, soot, particulate matter from the chimney.

They can be divided into three groups of fuel combustion products:

The first group is formed by the gaseous phase of combustion or pyrolysis due to incomplete combustion of fuel (products of incomplete combustion (PCC)):

  • soot and organic carbon particles are formed during the combustion process and from gaseous starting substances;
    • Condensed heavy hydrocarbons (tar) are an important, and in some cases, the main source of total particulate emissions from small-scale solid fuel combustion appliances such as fireplaces, stoves and older boilers.

    The next groups (second and third) may contain ash or cenospheres particles, which are mainly formed from minerals in the fuel. They contain oxides and salts (S, Cl) of the metals Ca, Mg, Si, Fe, K, Na, P, heavy metals and unburned carbon formed as a result of incomplete combustion of carbonaceous materials, black carbon or elemental carbon.

    Particulate matter emissions from solid fuel boilers largely depend on the combustion conditions. Optimization of the solid fuel combustion process through the establishment of continuously regulated conditions (automatic fuel supply, distribution of combustion air) leads to a decrease in the emission of total suspended particles and a change in the distribution of particulate matter.

    As you can see, boilers can have a wide range of particulate matter emissions, and these emissions can be divided into filtered and condensed fractions. The proportions vary, and the determination of particulate emissions is highly dependent on the measurement method.

    Reduction of emissions from the combustion process can be achieved by preventing the formation of such substances (primary measures) or by removing pollutants from the exhaust gases (secondary measures).

    Primary measures have several general possibilities:

    • changing the composition of fuel and improving its quality; preparation and improvement of the quality of solid fuels, in particular, coal (in relation to S, Cl, ash content and fractional composition of fuel); changing the granulometry of fuel by pressing - briquetting, pelletizing; preliminary cleaning - cleaning by washing; selection of size according to the needs of heating devices (furnaces, boilers) and control of its granulometry; partial replacement of coal with biomass (implementation of co-combustion technology, which reduces the amount of SO2, NOx), use of combustion modifier; catalytic additives and S-sorbent additives (limestone, dolomite), reduction and change of moisture content in the fuel, especially in the case of solid biomass fuel;
      • replacement of coal with modern secondary solid fuels, biomass;improving the design of furnaces; introduction of advanced technologies in the design of boilers.

    Additional emission reduction measures: For small combustion plants, secondary emission removal measures can be applied, especially for PM. Thus, emissions of PM-related pollutants such as heavy metals, PAHs and polychlorinated dibenzoparadioxins and furans (PCBs/F) can be significantly reduced by removing them together with particulate matter.

    For particulate matter, the following options can be considered:

    • dust settling chambers: self-distribution is characterized by low collection efficiency and is inefficient for small particle fractions;
      •  

      Emissions from burning different types of fuel

       

       

      From the table, we can see that wood fuel (primarily pellets and briquettes) has more advantages in terms of air pollution compared to fuel oil (especially coal), since it has an almost minimal effect on greenhouse gas emissions, primarily CO2.

      Unfortunately, it is impossible to completely eliminate the formation of suspended solid particles during the combustion of solid fuels. If at large boiler houses, due to the improvement of dust collection units, cyclones, construction of high pipes, etc., the concentration of solid particles can be significantly reduced, then for small boilers there are only two solutions :

      Use of high-quality low-ash dry fuel

      When it comes to a more environmentally friendly type of fuel - pellets, the main quality criterion is the ENplus certificate. At the same time, ENplus is not just a standard that regulates the physical and chemical properties of pellets, but a whole system that controls quality along the entire chain from raw materials to the end consumer, which sets the most stringent requirements for the quality of wood pellets and divides them into 3 classes.

      EN plus – A1 - The most stringent requirements are imposed on this pellet standard. They can be used only for domestic purposes. The ash content requirements are very strict - 0.5% for coniferous pellets and 0.7% for pellets from deciduous trees.

      EN plus – A2 - The plus grade - A2 can already be used not only in the private sector, but also in boiler houses. The ash content of these pellets can reach 1%, and the pellets can be obtained from mixed tree species, while the first grade pellets are obtained only from a certain species.

      EN-B-Grade EN-B is an industrial or industrial pellet that can be used in thermal power plants. The requirements for them are less stringent. But absolutely all pellets are subject to the rule that they should not be made from chemically treated wood.

      For each grade, there are parameters such as bulk density, diameter and length, and calorific value.

      Quality pellets have a shiny surface without cracks, which indicates compliance with production technology. The color of wood pellets alone cannot serve as a quality criterion and can only determine the raw materials used by the manufacturer. Also, the color can tell about storage and transportation conditions.

      If you fill the pellets with water, after a while they should turn into a mushy mass. If this does not happen, it indicates the low quality of the raw materials and the use of external chemicals by the manufacturer. Also, the use of this method makes it possible to determine the volume of heavy particles, which indicates the presence of dust and sand in the pellets.

      To test the pellets for strength, a lignotester is used, in which the pellets are loaded to 70 mAtm and placed in a fast air stream. After that, the weight of the pellets before and after the test is compared. High-quality pellets lose no more than 2.3% in weight. In general, the harder the pellets, the better, since soft pellets crumble when overloaded into the hopper and fed into the burner area.

      As a rule, pellets smell like the wood from which they were made or do not smell at all. On the other hand, pellets, during long-term storage, absorb moisture from the surrounding air and, accordingly, odors.

      When choosing firewood as a fuel, you need to remember that for optimal combustion and efficiency of your boiler, you need to use high-quality, well-dried firewood for at least six months in a well-ventilated room or under a canopy naturally. The moisture content of firewood should be more than 30%.

      Amber content is one of the main indicators that determine the quality of coal. The fewer mineral impurities the coal has, the fewer harmful substances are released into the atmosphere. For high-grade coal, the percentage of ash content is approximately 25%.

      For the most efficient combustion of biofuels such as wood chips, it is advisable to use boilers with a chamotte furnace, which provide high-temperature combustion of fuel. Such are the biofuel boilers of the ALTEP BIO model.

      Introduction of new combustion technologies

      The operation of any solid fuel boiler involves such processes as ignition, combustion and smoldering. The buffer capacity of the ALTEP heat accumulator will help to minimize the smoldering process (and together with it significantly reduce the amount of harmful emissions). Its use will provide:

      .

      • optimal combustion process of solid fuels;
      • increase the system operating time on a single load;
      • increase in boiler efficiency.
      The use of a torch burner will also help to ensure long-term fuel combustion. A dosed supply of high-quality fuel to the combustion zone can make the entire process of operating heating equipment more automated and preserve the ecological balance of the environment.

      Boilers with automatic fuel supply have a wide range of capacities (both for domestic needs and industrial scale). According to the international standard GOST 33016-2014 (EN 303-5:2012), when ALTEP boilers operate in compliance with all the manufacturer's requirements for connection and operation, using a high-quality type of fuel (in particular, pellets), the value of permissible emissions does not exceed the norm.

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      Type of fuel

      Air emissions withouttreatment systems, tonsn per 1 tands. tonsnnat ofural fuel
       

      CO2

      NO2

      SO2

      Solid particles

      TOTAL

      Wood briquettes, pellets

      4.68

      9.31

      0.28

      4.11

      18.38

      Wood wood

      4.9

      9.4

      0.3

      4.3

      18.9

      Wood sawdust

      5.0

      9.6

      0.5

      5.0

      20.1

      Wood waste, trimmings

      5.2

      9.9

      0.4

      5.2

      20.7

      Fast-growing wood

      4.8

      9.5

      0.0

      8.4

      22.7

      Chips, knots, bark

      5,6

      11.4

      0.8

      13.4

      31.2

      Mazut

      5.20

      5.20

      35.30

      0.30

      46

      Peat briquettes

      8.04

      26.81

      3.00

      13.02

      50.87

      Brown coal

      9.58

      63.56

      9.20

      65.32

      147.66