How to raise the temperature in a solid fuel boiler

HAPAI Solid Fuel Gravity Circuit Seminar

Automatics for solid fuel boilers: how to make the heating system with a CT boiler efficient?

In this article we will tell about how to make an effective heating system based on solid fuel boiler.

Boiler. It is no secret that solid fuel boilers vary greatly in the level of efficiency. But it is not necessary to focus on the price, brand name and country of origin to choose an efficient boiler. The efficiency is determined by such factors as the design of the heat exchanger and the boiler in general, the method of combustion (classical or pyrolysis), the size of the charging chamber, the duration of burning for one load, etc. д. Exactly these factors influence the efficiency of the boiler, the temperature of the flue gases and their qualitative composition.

Fuel. Quality and type of fuel also significantly affects the operation of solid fuel boilers. From good dry wood (large lumps of wood) much more heat and much less smoke and soot than from damp twigs, and the duration of combustion will differ at times. As for the good coal, it does not compare with the best quality dry wood. On coal any boiler, regardless of design, gives more power and works much longer than on wood.

Optimal mode of operation. The most efficient operation of the solid fuel boiler. at close to maximum loads: in this mode, the fuel burns absolutely without residues, the composition of the flue gases meets the highest environmental standards, and the heat exchanger of the boiler produces the highest possible efficiency.

But this mode of operation of the boiler is only possible during the heating system run-up, that is, when you have melted a cold boiler and it is still cool in the house: the boiler heats up, there is an intense process of heating the heating system and the room. Then, having achieved the desired temperature in the room, you set the boiler to moderate combustion mode (maintenance mode), so as not to overheat the boiler, the heating system and the house, and not to waste fuel. From this moment on any solid fuel boiler, both good and not so good, reduces its efficiency: the combustion air goes into the furnace less, fuel burns more slowly, the boiler temperature decreases and for some time is kept at the same level. This changes the qualitative composition of the flue gases: in addition to the basic components of smoke. CO₂ and CO₂O, a large amount of soot (you can tell by the color of the smoke) and CO (carbon monoxide), and other harmful impurities appear. Soot and carbon monoxide are nothing but unburned fuel that we throw into the sky.

In boilers with automatic fuel supply, such as pellet, diesel or gas, it is very easy to achieve the optimal mode of operation, or rather the optimal heat output. All you need to do is to reduce the amount of fuel supplied. The amount of air, which is fed into the furnace, will also be reduced, but the proportional fuel-air ratio will remain the same: less fuel and air less heat, and vice versa.

But it is not so easy in solid fuel boilers we have learned how to regulate the air supply, but the fuel is already fed into the furnace, enough time has passed since kindling and the whole volume of the wood logs is covered by the flame, that is the logs are heated to a certain temperature, and their whole surface began to actively release gaseous combustible chemical compounds. Reducing the amount of air, we leave some of the combustible chemical compounds without oxygen, that is, they simply do not burn and, under the influence of high temperature, converted into gaseous state, volatilize into the atmosphere through the chimney. It is as if we in a gas burner broke the gas-air balance, then part of the gas would fly into the atmosphere, while the gas flow rate would remain the same and the amount of heat would decrease.

The obvious conclusion is: the fuel in the boiler should be completely burned. But then what to do with the excess heat??

Storing up extra heat. Since ancient times people have learned to store and conserve heat, and they did it quite simply: in a stone cave or clay hut they left only openings for ventilation, so as not to suffocate on the burning fire, and the fire surrounded the perimeter around the stones heated stones long remained warm, after the brushwood in the fire burned out. Later, people began building massive stone and later brick stoves to heat their homes and cook food. Often these stoves took up half the house, which was not very convenient, but due to its weight the stove heated the house long enough.

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How to store heat in modern homes, the size of which has increased significantly, and the number of rooms in them (furnace heating is effective only within the room in which the furnace is located)?

We can use specially designed equipment heat accumulator that is a well insulated buffer tank for the storage of hot water (coolant). We will start the boiler at maximum power (i.e. in the optimal mode for it), at which it will operate for the entire cycle until all the fuel loaded in it is burned out. And the excess heat will be accumulated in the heat accumulator. When all the fuel is burned out and the boiler extinguishes, the heat in the room will come from the buffer tank. And only after the heat reserves in the buffer are depleted, we need to heat the boiler again.

Heat accumulator Hajdu

And to fill the accumulator we will use the Laddomat thermostatic mixing valve, which was also specially designed for this purpose. It will redistribute the flow between the boiler, buffer and heating system by controlling the temperature of the thermal fluid using its integral thermocouple.

Laddomat 21-60

At the start of firing up the boiler, the Laddomat will pump the water coolant in a small circle and return the water back to the boiler, helping it to quickly reach maximum efficiency. By the way, performed by the Laddomat’he heated water in the boiler return line prevents undesirable temperature fluctuations in the boiler, protecting it from corrosion.

Once the boiler is operating, the Laddomat will supply heat to the heating system (radiators, underfloor heating, etc.).д.) and store the excess heat in the heat accumulator.

boiler system. heat accumulator. Laddomat

In addition, the Laddomat will protect the boiler from overheating. Imagine that the electricity in the house is out, not such a rare occurrence in our valley. It is good, if there is a diesel generator. And if it doesn’t.? In automatic boilers, the fuel will simply stop flowing into the boiler, and it will turn off. And what about the wood or coal boiler, it can not be completely shut off? In this case, the Laddomat is equipped with a self-circulation system, thanks to which it will continue to remove heat from the boiler even in the absence of electricity until the boiler cools down or until electricity becomes available.

ATMOS boiler with heat accumulator and Laddomat

It is worth noting that by adding an automated system (such as Thermomatic EC Home) to the duo, which will regulate the flow of heat into the home heating system, we achieve an optimal indoor climate at the lowest possible fuel consumption.

The reason is the high inertia of the boiler. The boiler can’t go out quickly if there’s a sudden loss of heat. The coolant in the boiler boils and the increased pressure tears the boiler.

Modern heating systems are energy dependent. They have a circulation pump, or even more than one pump.

A circulating pump circulates the coolant in the heating system and boiler. If the circulation stops, the solid fuel boiler will boil over.

For this reason, many people like a gravity or gravity heating system. It has no elements that need electricity. This is the only advantage of the gravity circulation system. I can’t even imagine what it takes to make a boiler boil with this type of heating system.

Solid fuel boiler works continuously. It cannot be stopped quickly like a gas or liquid fuel boiler. It also gathers temperature slowly, as the fuel burns out. If the boiler stops moving fluid, it will boil and collapse, explode.

In the absence of control the coolant is heated to a maximum boiler temperature of 95C. But modern solid fuel boilers allow you to control within certain limits the temperature of the coolant by regulating the air supply with a valve.

Regulation of the temperature of the solid fuel boiler is carried out by changing the air supply into the combustion chamber of the boiler. There are two ways of such regulation: with the damper and thermostatic draught regulator, using the fan and automatics (controller) that smoothly changes its speed.

temperature, solid, fuel, boiler

In the absence of control the heating medium heats to a maximum temperature of the boiler. 95C. But modern solid fuel boilers allow you to control the temperature of the coolant within certain limits by regulating the air supply with a valve.

How to heat properly?

The coal stove or boiler is heated in this sequence:

  • open the furnace door and close the ash door;
  • Paper is placed on the grate and wood chips, oilcake or other flammable material is placed on it. A small quantity of firewood is put in the form of a hut or a well. Light the paper;
  • Close the firebox hatch and open the ash-pan door. Every time before opening the firebox door, close the ash-pan door and after closing it, open it;
  • after the burning of the wood filler, a thin layer of fine coal is placed on it;
  • after the coal burns through, you need to stir it with the poker to prevent it from baking. Otherwise the furnace will not receive air;
  • On the rancid fine coal lay the main fuel. coal of coarse fraction with the layer thickness up to 60 cm;
  • The ash-pan flap is slightly opened so that the optimum combustion mode is achieved in the combustion chamber.
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When firing up a forced-air boiler, instead of opening the damper, turn on the controller that controls the fan and set the desired temperature of the coolant on it.

Why a solid fuel boiler won’t get up to temperature and can’t heat the house?

Solid fuel boilers in Ukraine began to be mass installed only a few years ago. Exactly today passes the peak of demand and popularity of these boilers, due to which, they began to install even independently, without the help of specialists. And to understand a rather complicated heating system is not for everyone. And in the process of operation can be a problem, the source of which you need to know immediately. In this article, we will answer the question: why does the solid fuel boiler not heat, or does not reach the desired temperature?? A very topical issue, the answer to which not even all experts know.

Rules of operation

In order for the solid fuel boiler to work safely and efficiently, you should follow some simple rules when operating it:

  • Install only on non-combustible materials. Under the base of the device should be placed a metal sheet of thickness 0.6-1 mm with an asbestos or basalt cardboard backing of at least 3 mm. The metal sheet must be not only under the device itself, but also protrude from the front side by 0,5 m.
  • Do not use flammable liquids for kindling.
  • Air out the firebox for 10-15 minutes before ignition.
  • Keep the firebox hatch tightly closed during operation.
  • Do not leave unattended for long periods of time.
  • Periodic cleaning of the chimney.
  • At the end of the heating season to lubricate the moving parts of mechanisms of the device with the graphite grease.

Problems of slow-burning boilers

During the operation of combustion boilers, such as Stropuva boilers, the following problems can arise:

  • Detonation. Most often this phenomenon occurs at the first start of the device. The process is accompanied by humming sounds and smoke. Detonations are caused by too high draught in the chimney. The situation can be saved by installing a chimney draught regulator. This device automatically reduces the air supply.
  • Black tar comes out of the bottom door. Tar production in the solid fuel boiler is too high if the temperature in the combustion chamber is below 55 degrees. In most cases the problem can be solved by increasing the set temperature on the boiler regulator. In some situations, the intervention of a specialist will be required to balance the system. The cause of large amounts of tar may also be low-quality fuel.
  • Fuel burns faster than the minimum time. The reason may be too high heat consumption (mismatch between the output of the installation and the volume of the room) or poor fuel quality. Installation of additional heaters, measures to insulate the room or switching to fuels with higher calorific value can solve the problem.
  • Poor regulation of temperature. The reason may be that the device is already working at 100% of its capacity or the chimney draught regulator is faulty. To solve the problem you can take the measures described in the previous paragraph or repair the draught regulator.

Operating temperature of the solid fuel boiler

Proper operation of a solid fuel boiler, depends on several important factors. In order to heat your home with solid fuel boiler was not only economical, but also harmless for the equipment and chimney, it is important to know about the useful temperature of the boiler on solid fuel.

When heating the house with a boiler on solid fuel, users often do not take into account the minimum temperature at the inlet to the heating system. When burning solid fuel in the furnace of the boiler, a high temperature is created, which releases products of fuel decay, in the form of pyrolysis gases. In this case the boiler must operate without oxygen starvation, the fuel in the boiler must not smolder for a long time, otherwise the walls of the furnace and the entire jacket of the heat exchanger will constantly grow a layer of tar. The chimney will further have a layer of unnecessary deposits in the form of tar. At temperatures below 100C, these products of decay of fuel do not burn out, part of them goes through the chimney into the atmosphere, and part of them remains on the inner walls of the boiler and chimney. The high sulfur content causes corrosion of the metal, especially in the part of the boiler closest to the outlet to the chimney. And since some of the combustion products are simply not burned in the boiler, you do not get the full thermal energy of the burned fuel T.е. In order to get the maximum thermal energy from the fuel, there should not be a long interruption of the air supply. How does this relate to the set supply temperature of the boiler?! At work of solid fuel boiler at least at 65C, in the furnace constantly keeps high temperature at which, for example the wood will burn out completely and transfer heat energy from one kg of 3,4 to 4,1 kW when at low working temperature the same amount of wood can give out half as much heat, and useful highly calorific products of decay of fuel only harm the boiler and chimney, thus from a chimney will leave much harmful СО2. Therefore, no matter how your solid fuel boiler is controlled with a mechanical draught regulator with a chain, or an electronic control unit with an air blower, it is important to set the boiler to 65C. For example: if the temperature is controlled by a mechanical regulator, when the boiler reaches 65°C, the flap that lifts the draught regulator should not be completely closed, but should be slightly ajar to keep a small amount of air in, which will not allow the fuel to heat up further, but will also keep a small flame to prevent the fuel from smouldering. If the temperature of the boiler is controlled by electronic automation with a turbine, when heating with wood or all kinds of fuel briquettes, set the automation with minimal pauses of air supply, after the boiler has reached the operating mode 65C. In this case you get the maximum efficiency of fuel combustion, dry and clean furnace of the boiler, a clean heat exchanger without tar, which is difficult to get rid of, long-term operation on a single load of fuel, a clean chimney, a boiler without a smell of burning, consistently high boiler efficiency, because the walls of the heat exchanger, having a layer of tar reduces the efficiency of the boiler.

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The second important factor for the correct operation of the solid fuel boiler is the temperature of the water coming from the return of the heating system into the boiler. The minimum temperature should not be below 55C. At high temperature in the boiler’s furnace, if the incoming water is less than 55C, there is a possibility of condensation on the furnace wall at a high temperature difference. The lower the temperature of the coolant entering the boiler, the greater the amount of condensate. The damage of water on the boiler walls will cause corrosion of metal and weld seams. When installing a solid fuel boiler, it is strongly recommended to install a three-way mixing valve, which will protect the solid fuel boiler from condensate and will significantly prolong the boiler lifetime. Its work is to mix two streams, the coolant in the supply from the boiler having a high temperature and the coolant from the return heating system having a temperature below 55C, in case the coolant from the heating system has more than 55C three-way valve fully opens. And when the boiler is just getting a temperature, the three-way valve is closed, in this case, the coolant circulates in a small circle, allowing the boiler to quickly and smoothly enter the operating mode. In some cases where the installation of a three-way pre-regulated valve is not possible, e.g. in gravity heating systems without the use of a circulation pump, we recommend to make a small circulation loop with a balancing valve to heat the water coming from the return of the heating system, i.e.к. In gravity systems the water circulates much more slowly and consequently cools down more quickly.

Proper operation of the solid fuel boiler is to maintain minimum operating temperatures. To do this, it is important to select the correct capacity of the boiler, and do the installation with the observance of mandatory standards, and of course with the ability to control the temperature in the heating system, autonomously without reducing the operating modes of the boiler on solid fuels. There are many schemes for installing a solid fuel boiler, which allow you to regulate the temperature for comfort in the house regardless of the outside temperature.

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