Waste heating. Boilers for wood chips and wood waste. How does a wood waste boiler work?

It is unfortunate that the choice of waste-fired boilers for domestic use in the Russian market is very small. Such heating devices, subject to an affordable price, could not only greatly facilitate the living of people in the outback, but also reduce the unjustified consumption of such a valuable resource as wood.

Irrevocable combustible production waste is always of interest as a cheap fuel for industrial and domestic needs. In the course of primary woodworking (roundwood sawing), such waste is sawdust, which is formed in considerable volumes.

Their periodic removal or disposal results in significant costs, and their permanent storage at the production site is fraught with sanctions from environmental and sanitary and epidemiological control authorities. The use of sawdust, taking into account their constant formation, for heating private houses and cottages looks very attractive.

Given the specifics of the fuel, it is useful to first carefully familiarize yourself with the characteristics and features of operation. In addition, a few words must be said about the fuel itself.

Fuel supply

So, for constant heating, sawdust should:

• Formed in the volumes necessary for heating. It makes no sense to install such a boiler if there are not enough of them. This should be the first thing to pay attention to. For example, a 25 kW boiler consumes up to 40 kg of sawdust per hour during the heating season. On the other hand, an excessive amount of sawdust in the warehouse is also undesirable, since their storage sharply worsens the quality: sawdust becomes dense and damp, burns poorly with low heat transfer.
• Get by cheap. Since the sawdust is usually supplied by the manufacturer free of charge, the only cost will be the transportation costs for delivering them to the house for heating. It should be borne in mind that they have a low density and are inconvenient for transportation.

Calculate how much the delivery of fuel will cost you, and what, accordingly, will be its price.

Fuel Requirements

The efficiency of the boilers directly depends on the moisture content of the sawdust. The use of dry shavings and sawdust from carpentry as fuel does not cause problems. The main mass of sawdust is, as noted, the waste of roundwood sawing shops.

The production waste of sawing round timber at band sawmills is small (up to 0.3 mm) sawdust with a moisture content of up to 80%. Even with a constant forced air supply to the furnace, such sawdust burns very slowly, since it takes time to dry them. An even greater problem during combustion is raw, long-stored sawdust, compacted into a damp dusty mass.

Such fuel should be burned in a certain mode:

• Dry and raw fuel must be supplied to the combustion chamber in a ratio of 3:1.
• The supply of raw fuel can only be started when the boiler has reached full power after ignition.
• Constantly forcibly supply air with a fan into the combustion chamber.

Advantages

The working process is based on the thermal decomposition of wood, called pyrolysis. In the smoldering mode, pyrolysis gas is released in the gas generation chamber, which then burns out in the combustion chamber under conditions of forced air supply.

The undeniable advantages are

• High efficiency (up to 85-90%).
• High profitability (up to 8-12 hours of heating on one boiler load). Pyrolysis boilers are 3-5 times more economical than classic wood-burning boilers, and 10-11 times more economical than gas boilers, with approximately the same heat release.
• Rapid heating of the room (30-40 minutes) after ignition of the boiler.
• Simplicity and reliability of a design.
• Low fuel consumption.
• Low fuel cost.
• Possibility of switching to the mode of a conventional wood-burning boiler.
• Independence of power from the grade of raw materials. The boiler, in addition to sawdust, can work on bark, wood chips, branches, wood.
• Ease of maintenance and cleaning of the boiler.
• Environmental Safety.
• Ease of operation allows you not to spend money on expensive training of boiler room personnel.
• Due to the low cost of sawdust and high efficiency, such boilers pay off very quickly.

Configuration options and operating principles

Consider several options for boiler equipment designed for heating a residential or country house.

Boiler plant

The most convenient and modern is an automated water heating plant that runs on sawdust, wood chips, shavings. If there is a large volume of the coarse-fraction part of the fuel, you can purchase a crushing machine for processing the coarse fraction into a fine one.

The installation includes the following nodes:

• Fuel bunker
• gas generator
• Hot water boiler (combustion chamber and heat exchanger)
• Automatic control unit

The design of the dwelling can provide for various options for placing equipment: completely outside or inside the room, as well as with the removal of individual units to the outside.

Description of the work process:

Sawdust is unloaded into the heating bunker by a dump truck (tractor, front loader). To prevent sawdust from caking, a tedder is provided in the bunker for their periodic loosening.
Through a conveyor (belt or screw), they are fed into the gas generation chamber, where, in the slow burning mode, thermal decomposition of the fuel occurs with the release of pyrolysis gas. Fuel is supplied to the conveyor and to the gas generation chamber automatically.

The pyrolysis gas coming from the gas generator into the combustion chamber burns out completely, heating the water. The content of unburned components in flue gases is minimal: carbon monoxide is only up to 1%, nitrogen oxides are up to 300 mg/m³. Hot air is supplied to the combustion chamber by a fan, which contributes to the deep burnout of the pyrolysis gas components.

The automation system controls the following processes:

• Fuel supply to the gas generator
• Hot air blown by a fan in proportion to the volume of fuel in the combustion chamber
• The temperature of the coolant and its change
• firefighting

Boilers on and sawdust HARGASSNER (Austria) are typical equipment of this level used for heating private houses, hotels, offices, cottages in Europe. The power of such boilers is 25 - 55 kW, the heated area is 200-600 square meters. m.

domestic producers

Domestic manufacturers also offer a wide range of sawdust and pellet boilers for heating individual housing and small industrial premises.

The offered boilers are mainly pyrolysis boilers operating in automatic mode. Technologically, the combustion process is similar to the one above. The only difference from imported equipment is that Russian boilers, as a rule, are not provided with automatic fuel supply lines.

Automation regulates the operation of the blower fan for a stable set temperature of the coolant, which is set by the control units. In case of scheduled or emergency shutdown of the fan, the boiler continues to operate at reduced power. Laying sawdust, shavings and other wood waste burns out in them within 4-12 hours, depending on the selected combustion mode.

Long-burning mine boilers

Mine long-burning boilers (Kholmov's boilers) deserve special attention. These are pyrolysis boilers of a special design. Their constructive advantage is that the fuel placed in a special shaft partially dries up, which makes it possible to use high-moisture sawdust for heating.

• Automation (controller) controls the combustion process, the set coolant temperature and the operation of the centrifugal pump.
• The safety system is provided with an emergency boiler cooling circuit and a safety valve.
• Maintenance of the boiler takes a few minutes 1-2 times a day.
• The use of such boilers allows you to heat cottages and small industries with an area of ​​​​60 -250 square meters. m.

Own designs

The design of such boilers offers a lot of home-grown "homemade" ones on the network. Without focusing on creative innovations in the advertised devices, we note that such equipment cannot be reliable and durable, in principle.

The materials from which it is made most often do not meet the operating conditions, the structures themselves are primitive, they lack the most elementary automatic control and security systems. At the same time, a fully equipped factory boiler for sawdust or pellets with a capacity of 20 kW, with a guarantee, capable of heating a cottage or country house, costs only about 40-50 thousand rubles. Agree, this is not the amount, saving which you can risk your own health and housing.

Boilers operating on sawdust and other woodworking waste are today the most cost-effective equipment for heating private houses. When deciding on the choice of such equipment, special attention should be paid to the availability of the required volume of fuel that meets the moisture content. If it is planned to burn sawdust with a moisture content of more than 55-60%, then they should not exceed 20-25% of the material loaded into the furnace. The main fuel should be wood waste with a moisture content of up to 20%.

Waste-fired boilers is a collective non-formalized term that combines boilers, furnaces and boiler units - heat recovery units of different design, thermal power, efficiency, purpose and popularity, which ensure the incineration of waste of various origins using the heat obtained during combustion instead of expensive and environmentally unsafe burial in special polygons. The most commonly used waste boilers in the developed world include:

• waste incineration boilers, furnaces and boilers on the waste of industrial enterprises and boilers / furnaces / boilers on human waste - as a rule, municipal solid waste;
• stoves and boilers for woodworking industry waste - wood-fired boilers, boilers for wood chips and pellets (specially compressed granules of pre-shredded waste from woodworking enterprises);
• boilers on waste products of the oil refining industry (boilers and air heaters on waste oils - motor, industrial, turbine, hydraulic, transmission) and oils of animal / vegetable origin.

The main characteristics of any boiler on waste include:

• efficiency factor, which ranges from 30-40% for waste incineration boilers to 80-90% for pellet boilers (condensing type) and mining boilers;
• specific cost of obtaining 1 kW/kJ/kcal of heat by burning a unit volume/mass of waste;

Important: The specific cost of obtaining 1 kW / kJ / kcal of heat is determined not only by the calorific value of the waste and the efficiency of the waste boiler, but also by:

the cost of additional energy used for waste incineration - fuel (gas, fuel oil, waste) used in the ignition and stabilization burners of waste incineration boilers, electricity from compressors / fans that supply primary and secondary air to the combustion chamber, electricity from chamber pushers and electric motors for rotating waste incineration hearths boilers, electric power of screw mechanisms for loading and cleaning grates of pellet boilers, electric power and fuel of systems for multi-stage cleaning of exhaust gases of waste incineration boilers, etc.;

the cost of delivery and preparation for waste incineration;

the cost of cleaning the combustion chamber and smoke channels, as well as the cost of measures for the disposal of slag formed after combustion;

the initial cost of the waste-fired boiler, the amount and frequency of depreciation charges;

the cost of automation and / or the work of maintenance personnel, etc., etc.

the cost of a furnace/boiler unit/boiler on waste and related equipment/structures/devices/measures that provide a full cycle of waste incineration with slag disposal and purification of burnt gases from impurities to MPC established by international and/or current national legislation.

Waste incineration boilers.

Waste incineration boilers, less often waste-fired boilers in Russia are used in waste incineration plants, sometimes in large centralized boiler houses. Typical waste incineration boilers are chamber type, usually with pushers that provide feeding / mixing of waste and cleaning the grate from slag, or are made like rotary hearth furnaces. To ignite and stabilize combustion in waste boilers, gas-oil, oil-fired or waste oil burners are used, more complete combustion is ensured by forced air supply to the combustion chamber (from the loading window, from the bottom and sides), as well as temperature zoning (in rotary kilns / waste boilers) with the provision in zones of a temperature not lower than 1200 degrees Celsius for the afterburning of soot with benz (a) pyrene and dioxins absorbed in it and a temperature of 1500-1600 degrees Celsius, at which the maximum possible complete decomposition / oxidation of dioxins, furans and carcinogenic substances.

As a rule, after the waste furnace/boiler, reactors/scrubbers are integrated into the process chain for cleaning exhaust gases from solid inclusions, organic and inorganic acids, nitrogen dioxide, sulfur compounds, as well as electric filters for the final purification of burnt gases from fine particles of slag and fine ash. inclusions.

The norms formalized back in the USSR determine the possibility of locating waste incinerators on waste no closer than 300 m from residential buildings, and furnaces / boilers / boilers on waste must be equipped with an effective system for cleaning burnt gases to the established maximum concentration limits for NH3, HF, HCl, NOx, SO2, CO2, CO, dioxins and furans, soot, etc.

The main problems of waste incineration boilers in Russia:

the calorific value of Russian municipal solid waste is 900-1300 kcal/kg, while the waste in the EU countries, the USA, Canada due to the higher content of packaging combustible materials and the lower content of food waste (no more than 15-20% compared to 35-40 % in Russia) have a calorific value of 2200-2600 kcal/kg. The low calorific value of Russian waste determines the low temperature level in the combustion chamber (at the level of 800-1000 degrees), incomplete combustion of waste, a large amount of slag (30-40% of the volume / mass of the load) and high toxicity of exhaust gases, which necessitates the use of whole complexes for post-treatment of gases before their release into the atmosphere and disposal of slags at specially designated landfills for these purposes;

the absence in Russia of preliminary sorting of waste according to the places of their collection, as is practiced in the EU, the USA and other countries, makes it practically impossible to determine the approximate composition of waste, their calorific value, correction of the combustion process, as well as the presence of ferrous and non-ferrous metals in slags, which it is advisable to separate from the slag before its disposal;

Waste-fired incinerators are large-scale units that are expensive in terms of initial investment and operating costs, and their installation in enterprises, waste incinerators or boiler houses requires a large number of permits from the relevant authorities;

Woodworking industry waste boilers are currently recognized by the EU as promising heat generators, oriented to use both in local heating systems and boiler heat networks (the thermal power of modern woodworking industry waste boilers varies from 2-3 kW to 200 kW or more). If we abstract from typical solid fuel boilers, inefficient, with manual loading of fuel and cleaning of the combustion chamber, which are still being sold by a number of manufacturers on the market of thermal equipment in Russia, then it should be recognized that over the past 2-3 decades, boilers using waste from the woodworking industry (wood, wood chips, pellets) have passed the next stage of evolution and today they are characterized by comfort in operation and efficiency in burning wood waste.

Rice. Typical solid fuel boilers.

Waste boilers from manufacturers in Germany, Finland, Sweden have an efficiency of 80 to 96% (in condensing boilers), equipped with systems for automatic fuel loading, combustion chamber cleaning, control and management of the combustion process and removal of burnt gases (see videos below) .

Video of the operation of an automated wood-burning boiler Buderus AG, part of the Bosch Thermotechnik division production and commercial groups Bosch Group .

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Video of the operation of the automated pellet boiler Buderus AG.

The main difficulties in arranging heating with wood / pellet boilers in Russia:

calorific value of coniferous firewood 7.5 - 8 MJ / kg, pellet - 6 MJ / kg, waste oils - 34 - 35 MJ / l, diesel fuel - 33.5 - 34 MJ / l, i.e. to obtain one power of thermal energy it is necessary to burn 1 liter of mining / diesel fuel, 5.5 kg of pellets or 5 kg of softwood or hardwood firewood. At the cost of a kilogram of firewood / pellets from 6 rubles, the cost of a liter of mining is 6.5 rubles. and a liter of diesel fuel 29 rubles. in the Moscow region, with equal boiler efficiency, this will determine the cost of 1 kWh of energy 3.07 - 3.03 Rub. / kWh for diesel fuel boilers, 0.68 - 0.66 Rub. / kWh for mining boilers, 2.85 - 2.68 Rub. / kWh for wood-fired boilers and 3.39 - 4.05 RUB / kWh for pellet boilers;

the calorific value of wood waste strongly depends on the moisture content of the fuel being burned, and therefore it is necessary to equip a special dry room for storing a reserve supply of firewood / pellets, preferably with control and correction of relative humidity, and the room should be located in close proximity to the boiler room and have a significant volume, sufficient to ensure the uninterrupted operation of the boiler on waste during the period of operation;

the cost of automated waste-fired boilers - wood and pellets, and even more efficient condensing type is very high, and the failure-free operation of automation is determined both by the quality of the manufactured components and the mechanism, and by the quality of the supplied electricity;

Typically for Russia, an increase in the number of pellet producers has practically no effect on their consumer value, which has been steadily increasing over the past five years.

Waste oil boilers.

Waste oil boilers are still considered one of the most economical heat generators in terms of initial investment and operating costs, and even in Russia, the cost of waste oil recovery remains relatively stable, due to significant costs for the disposal of waste oil from supplier enterprises and low demand compared to the current supply on the market. The main advantages of air heaters and mining boilers include:

• high calorific value of mining, comparable to the calorific value of diesel fuel;
• ease of automation, control and management of boiler equipment and the heating system as a whole, including remotely via the Internet, cellular networks 4G, 3G, EDGE from a PC, Netbook, AppleMacBook, Notebook, smartphone, communicator, iPad, iPhone and iPodTouch (see. );
• relatively low cost of modern boilers for mining and low operating costs for fuel, maintenance and depreciation of equipment;
• the availability of mining on the fuel market at the current moment and in the future, taking into account the fact that the annual accumulation of used oils in Moscow alone is more than 250 thousand weight tons and this value is constantly increasing.

BiComs Holding is the official distributor of the leading American manufacturer of waste oil heating equipment EconoHeat - OMNI USA, an authorized dealer of EnergyLogic (USA) and offers its compatriots - legal entities and individuals efficient and economical air heaters and exhaust boilers. BiComs Holding specialists will help you choose an air heater or a boiler to develop the required power, if necessary, design an efficient heating system, provide full information and advisory assistance during installation and operation, perform warranty and post-warranty (under the contract) maintenance of boiler equipment.

In the face of fierce competition, furniture enterprises and sawmills are forced to constantly optimize their costs. One of the ways to minimize them is to use our own wood waste for heating industrial premises. For this purpose, the enterprises are installing boiler houses operating on woodworking waste. Let's consider the principle of operation of such a boiler house using the example of the most common boilers of the KTU series from Teploresurs to date.

General scheme and principle of operation

It should be noted right away that the laying of fuel for heating occurs mechanically using a screw system or a hydraulic pusher. This eliminates the manual work of putting fuel into the boiler. Maintenance staff responsibilities include:

1. Boiler control

2. Regular filling of fuel in a special hopper, from which fuel is supplied to the boiler.

3. Cleaning the ash pan. In the advanced configuration, there is a function of mechanical removal of spent fuel residues, in the basic configuration, you have to do this work manually.

In the operation of the boiler, the following three stages can be distinguished.

1. Drying of fuel. Most of the waste comes from wood processing enterprises, therefore, they have high humidity. To ensure uniform and stable combustion, sawdust is dried on a grate.

2. CO isolation. Initially, a low temperature is maintained on the grate, due to which the sawdust, when burned, emits a maximum of carbon.

3. Afterburning of CO. The combustion product is fed into the afterburning zone and burns at a temperature of 900-950 degrees. This allows the process of carbon oxidation to take place.

This scheme allows you to significantly increase the efficiency of combustion and practically use the full potential of wood chips for space heating. This principle of operation is called layered combustion on a grate. The automatic air distribution also contributes to the combustion efficiency.

Security systems and automation

In order for the boiler to work in the safest way, the following protection devices are used.

1. Thermal insulation of the cladding.

2. Anti-explosion valves. Relieve excessive steam pressure.

3. Temperature sensors at the inlet and outlet of the coolant.

4. Flue gas temperature sensor.

All these elements help to effectively take care of the safety of the boiler and prevent possible dangerous situations, and, if necessary, give a signal and stop the operation of the unit. The rate of fuel combustion is controlled by dosing oxygen for oxidation. Feeding materials into the furnace is carried out using a screw system or a hydraulic pusher.

Benefits of using a sawdust boiler

As the main advantages, it is worth noting the low cost of fuel, compared with fossil fuels, and as a result, low operating costs. The ability to switch from one type of fuel to another (peat, sawdust, shavings, etc.) with minimal changes in the boiler settings is also a significant plus. Thanks to boilers of this type, it is possible to save significantly. This is especially noticeable if you have to heat large rooms. Purchasing fuel is also not a problem, most logging and wood processing companies will readily dispose of several tons of waste that must be disposed of.