What is a long burning pyrolysis boiler?

Imagine having a heating system for your house that not only keeps you warm and comfortable in the winter but also uses less energy, which lowers your carbon footprint and saves you money. Presenting the long-burning pyrolysis boiler—a contemporary marvel for insulation and heating in homes. However, what precisely is this cutting-edge technology, and how does it operate?

Fundamentally, a long-burning pyrolysis boiler is a kind of heating system intended to reduce its environmental impact and maximize energy efficiency. Pyrolysis boilers use the process of pyrolysis to extract energy from organic materials like wood pellets, chips, or logs, in contrast to traditional boilers that only use combustion to generate heat.

By breaking down organic materials chemically in the absence of oxygen, a process known as pyrolysis, combustible gases, liquids, and charcoal are produced. This procedure makes it possible to effectively extract heat energy from biomass in the context of a pyrolysis boiler, which is then used to heat water for home heating needs.

Being able to achieve longer burn times than traditional wood-burning stoves or boilers is one of the main benefits of a long-burning pyrolysis boiler. This is made possible by the pyrolysis process’s gradual and regulated gas release, which prolongs combustion and eliminates the need for frequent refueling.

Furthermore, rather than being thrown away, the byproducts of pyrolysis, such as charcoal and biochar, can be used as valuable resources. While biochar can enhance soil fertility and carbon sequestration, it can also be utilized as a high-quality fuel source and soil amendment that promotes environmental sustainability.

In understanding the concept of a long-burning pyrolysis boiler for heating, it"s essential to grasp its core principle: efficient and sustainable heat production. Unlike traditional boilers, these innovative systems utilize a process called pyrolysis, where wood or biomass is heated in a low-oxygen environment, breaking it down into gases and charcoal. These gases are then burned, releasing heat energy for heating purposes. What sets long-burning pyrolysis boilers apart is their ability to prolong the burning process, maximizing heat output while minimizing fuel consumption. This translates to cost savings for homeowners and reduced environmental impact due to lower emissions. In essence, these boilers offer a greener and more economical solution for keeping homes warm during colder months, aligning with the growing emphasis on sustainability in modern living.

Briefly about pyrolysis combustion

Pyrolysis is the slow breakdown of carbon fuel that takes place in an oxygen-free environment at high temperatures. Depending on the feedstock and the circumstances surrounding the chemical reaction, the result is either liquid fuel or combustible gas.

Boilers that use pyrolysis to heat produce and burn gas exclusively; thus, the term "gas-generating" or "gasifying." The first raw materials are fuel briquettes, coal, and dry firewood.

Citation. A large range of solid fuels containing hydrocarbon compounds are used in pyrolysis combustion. The conversion of used auto tires into liquid fuel or the incineration of waste in industrial gas generator furnaces are two examples.

The process of wood pyrolysis:

1. In a closed tank (reactor) is loaded with a certain volume of chopped wood or sawdust.
2. The metal vessel is heated from the outside to 500…900 °C, with a limited air supply through lances (blow holes).
3. The wood smolders and decomposes into hydrogen, methane, carbon monoxide, water vapor and carbon dioxide. At the end of the reaction, some ash remains at the bottom.
4. The resulting gas mixture is cooled, purified, then pumped into cylinders for further use.

Prior to being placed inside the gas generator, the wood is dried. If not, the pyrolysis reaction will slow down significantly, the heating energy will be used for the evaporation of water, and the result will be a pile of water vapor.

Keep in mind that wood gas is released during the burning of solid fuel, even when there isn’t a fire (see photo). Our other publication goes into further detail about pyrolysis.

2 types of gas-fired boilers

The only difference between the two units’ operating principles is how combustion is arranged. Any pyrolysis boiler consists of two chambers:

• fuelbox, where combustion takes place, decomposition of wood with the release of combustible gases;
• secondary chamber, where flue gases burn, releasing additional heat.

In other words, the independent combustion of fuel is the foundation for the pyrolysis boiler’s operation. As the wood burns, heat is released, heating the upper layers and releasing hydrogen and carbon monoxide. With the help of a different air supply, the mixture enters the secondary chamber and burns.

We chose to use the classification of the well-known Czech company Atmos, which has been producing two-chamber heaters for more than ten years, in order to provide a clearer description of wood and coal heat generators. Boilers are thus separated into two categories:

1. Conventional pyrolysis. Here the separate air supply is organized due to the natural draught of the chimney.
2. Gasifying models with forced supercharging with the help of a fan (or smoke pump), equipped with automatics.

Let’s examine each type in isolation, using the boilers "Atmos" as illustrations.

Principle of operation of pyrolysis unit

We’ll use the low-power Atmos DC15E model, which has a maximum output of 15 kW, for our description. Oriented according to the drawing, the interior of the pyrolysis boiler looks like this:

• spherical bodies of both chambers are welded from 6-8 mm thick steel, the upper one is a fuel hopper, the lower one is a combustion chamber;
• from the inside, the walls are protected by a fireproof ceramic shell (lining);
• a gas duct leads from the upper firebox to the lower compartment, the size of which is limited by the nozzle of the ceramic nozzle;
• The movable grate is integrated into the nozzle passage;
• separate air ducts are connected to the chambers from behind, the air supply is regulated by a mechanical thermostat (chain draught regulator) and a manual damper;
• the inner casing is surrounded by a water jacket made of 3 mm metal, covered with a layer of insulation and an external lining;
• in case of overheating a coil is installed inside the jacket – water circuit of emergency cooling of the boiler, the connections are brought out on the upper panel;
• on the back wall there are connection pipes for connection to the heating system and chimney;
• the role of the ash pan is played by the secondary afterburning chamber, where a protective ceramic element is placed, shown on the photo below.

Note: Despite being significantly less expensive, the pyrolysis heat generator designs of other European manufacturers, such as Buderus and Viessmann, are essentially identical to those of Atmos.

The DC15E solid fuel boiler operates according to the following scheme. After placing large logs in the firebox and lighting them, the main airflow passes through the damper located in the back wall. Additional procedures:

1. Firewood is burnt in the mode of intensive or medium combustion. Pyrolysis reaction starts, smoke together with flue gases moves to the lower chamber, bypassing the nozzle of the nozzle nozzle.
2. A share of the released heat is used to support the pyrolysis process, the other part is transferred to the heat transfer medium.
3. Thanks to the supply of secondary air, combustible gases are afterburning in the lower compartment, release heat, which is transferred to the walls of the water jacket.
4. Natural draught draws combustion products into the chimney.
5. After the fuel tab burns out, the boiler thermostat is activated, disconnecting the heating circulating pump.
6. In case of overheating, the water circuit connected to the water supply (not to the DHW network, as you might think) is activated. Cold water supply is handled by the thermal relief valve, which reacts to the signal of the temperature sensor.

The fuel box temperature reaches 800 degrees when the unit is operating at full capacity, and the manufacturer states that it reaches its maximum efficiency of 83%. The efficiency falls to 71% if the boiler is placed in the long burning mode and the air is "pressed" by the damper.

The cause is a reduction in the heat produced by burning wood directly, which lowers the temperature and slows down pyrolysis. The heater’s design and construction are shown in the video:

Description of gasifying heat generators

Though there are some notable variations, these boilers’ designs essentially mimic those of pyrolysis heat generators:

• primary and secondary air is blown by a fan, usually a smoke pump;
• Air flows are directed to the fuel from the side walls;
• The temperature of the coolant is controlled by the automation unit;
• The shape of the ceramic nozzle and the baffle in the secondary compartment have been changed;
• a heat-tube heat exchanger is installed in the rear part;
• The efficiency of boilers lies within 81…87%, the highest temperature of the flame torch is 1250 °C (data of the manufacturer "Atmos").

The gasifying heater works on the same principle: combustion occurs in the lower compartment, which doubles as a bunker for firewood and a gas generator. The combustion chamber’s high air flow rate causes a flame torch to form, the temperature to rise, and coal and wood to burn more efficiently.

There are subtle differences between gas-generator boilers from different brands, such as the fuel box’s shape, the chambers’ air distribution system, and the nozzle arrangement. In less expensive models, brick lining can be used in place of shaped ceramics; there is no water cooling circuit, and the metal is 4-5 mm thick.

Rules of operation

The manufacturers advise adhering to the following guidelines to get optimal heat output from the gas generator heater while using the least amount of fuel possible:

• use only dry firewood, permissible humidity 12…20%;
• When installing and piping the boiler, it is obligatory to use a three-way mixing valve or a complete device Laddomat-21 to maintain the return temperature at 65 °C;
• operating temperature of the heat carrier at the supply – 80…90 °C;
• the heat generator must be operated at a power close to the maximum capacity, the unit must not be operated for a long time in a low capacity mode (less than 50%);
• it is very desirable to fire with large logs, but not with round stakes;
• Together with pyrolysis boilers it is strongly recommended to use a buffer tank, which will accumulate excess heat energy;
• the requirement for the minimum volume of the heat accumulator – 25 liters for each kilowatt of heater capacity.

Justification. In the primary chamber during the fuel gasification process, condensate and tar will form if a cold coolant that is less than 65 degrees Celsius is added to the boiler tank. See a separate handbook on connecting TT-boilers for additional information on proper plumbing.

The efficient mode of boiler operation—intensive combustion with an outlet temperature between 80 and 90 degrees Celsius—determines whether or not a buffer tank is used. Under these circumstances, 86–87% high efficiency is attained. It is impossible to "smother" an air-powered heat generator; instead, the combustion efficiency will drop to 40–50%, similar to a homemade burzhuyka stove.

Real advantages of pyrolysis heaters

Let’s go over the benefits of gasifying boilers as stated by the sellers before sorting through the complete bikes:

• Pyrolysis heat sources are full-fledged gas generators, emitting combustible synthesis gas;
• The units are very economical and environmentally friendly due to their high efficiency;
• boilers burn coal and wood completely, practically without residue;
• burning time – over 10 hours (the most modest figure is 8 hours).

Advertisers and less than ethical manufacturers frequently draw comparisons between gas generator units and traditional direct-burning boilers, often overlooking the equally effective pellet heaters. However, this comparison is not entirely positive.

The opening claim is overly audacious. Recall that intense pyrolysis begins with high temperatures and an oxygen deficiency. What transpires in the boiler then? There is no smoldering because the fan fills the furnace with too much air. Naturally, synthesis gas is released, but fuel is also burned directly.

Let’s dissect the remaining benefits:

1. Claims about economy and environmental friendliness are not fairy tales. Due to the decent efficiency of the boiler better utilizes the energy of fuel and emits into the atmosphere much less toxic compounds – nitrogen oxide and carbon monoxide. Under 1 condition: recommendations on mode of operation and moisture content of firewood are fully observed.
2. The reasons for more complete combustion are dry firewood and forced air injection. If you put sawdust briquettes or dry acacia wood in a traditional turbo boiler, the ash residue will also be zero. A lot of light ash is simply blown by the fan into the chimney. So, this fact is not an advantage.
3. The duration of combustion depends on 2 factors: efficiency and capacity of the fuel compartment. In terms of efficiency solid fuel boilers lose to pyrolysis boilers by 10%, this is a small increase in the duration of work. The main factor is the volume of the combustion chamber, if it reaches 80 liters or more, the wood burns through in 6-8 hours.

Citation. The following is how Czech manufacturer Atmos puts the benefits of their heat generators (literally): long burning time – large fuel hopper. Thus, the statement regarding the length of operation is accurate; the cause, which is the furnace’s capacity rather than the fact that wood gas is being generated, is different.

Additionally, there are many urban legends regarding the cost-effective smoldering mode, which is just not present in pyrolysis units. The following is stated in the instruction manual for the Atmos DC15E: a drop in flame intensity causes an increase in fuel consumption and a decrease in efficiency.

Significant disadvantages of boilers

You can quickly identify the primary drawback of pyrolysis heat generators if you visit any online heating unit retailer and inquire about their price. The most affordable Russian boiler, the "Suvorov M" K-20 (20 kW), will set you back 1320 u. е., while an ATMOS DC 20 GS of the same capacity will set you back 2,950 u. е. In contrast, the cost of the Buderus Logano Logano S131-22 H, a traditional heater that is not inexpensive, is 1010 u. е.

Let’s go over some additional drawbacks of gasifying heat sources:

• 2 chambers, brick or ceramic lining plus a water jacket in the lower part of the body – these design solutions significantly increase the weight and dimensions of the units;
• high demands on the quality of fuel;
• Heat transfer medium with a temperature of 80 °C is rarely used for heating private houses, which means that an expensive heat accumulator + piping elements are required;
• ceramic lining parts are not eternal – overheating can crack the nozzle and it will have to be replaced.

Home craftsmen find pyrolysis boilers appealing, it must be said. However, it is very difficult to make such a unit by hand; you need to invest in materials and have experience. A heater cannot be produced for free. Welding a conventional or shaft boiler is significantly simpler.

Note: It appears that raw wood can still be used, based on the opinions of boiler owners posted on relevant forums. The procedure is as follows: dry logs are melted and heated in the unit, and then wet wood is added. However, the proportion of this fuel shouldn’t go above 30% to avoid soot and grime. Let’s hear what the specialist has to say about the video:

Pyrolysis boilers with long burn times are a novel way to heat your house effectively. These boilers use less fuel than conventional boilers because they can generate heat for longer periods of time by utilizing the power of pyrolysis. By converting biomass, such as wood, into combustible gases, this technology produces heat. Long burning pyrolysis boilers therefore use renewable resources and emit fewer emissions, which benefits the environment in addition to saving money.

The high efficiency of long burning pyrolysis boilers is one of their main benefits. These boilers are able to achieve far higher levels of efficiency than traditional heating systems because they are able to extract heat from the pyrolysis process. As a result, homeowners can enjoy a cozy interior while using less fuel, which will ultimately result in lower energy costs. Furthermore, pyrolysis boilers require less frequent refueling due to their longer burn times, which saves homeowners time and effort.

Moreover, by using biomass fuels like wood chips or pellets, long-burning pyrolysis boilers support sustainability initiatives. Because biomass is abundant and renewable, it is a more environmentally friendly option for home heating than fossil fuels. Homeowners may lessen their dependency on fossil fuels and lessen their carbon footprint by purchasing a pyrolysis boiler, which will aid in the fight against climate change.

To sum up, long-burning pyrolysis boilers are a promising development in residential heating systems. These boilers provide a sustainable and affordable way to heat homes during the winter months because of their high efficiency, long burn times, and use of renewable biomass fuels. In addition to saving money on their heating bills, homeowners can help create a more environmentally conscious and greener future by selecting a pyrolysis boiler.

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