Introduction
For most industrial and transport enterprises, the topic of waste disposal is one of the most acute and topical. Here we will talk about the disposal of used motor oils (hydraulic, motor oils up to 50SAE and transmission fluids), hereinafter OTM. Based on the combination of properties, we can classify substandard diesel fuels and vegetable oils as such.
The disposal of fuel waste for most enterprises is an expensive problem in financing the maintenance of collection, storage, transportation, processing and annealing points. After the abolition of energy supervision structures, the situation worsened due to the loss of unified control over the operation of equipment and the use of fuels and fuel waste at facilities. Partially, these functions were taken over by various departments, but, as usual in Russia, "but things are still there."
An insignificant part of HM is burned in poorly adapted boiler houses and furnaces, and a large part of HM is discharged into water bodies and sewers, onto the soil, and even sprayed into the atmosphere, which causes inestimable environmental damage. Only a tenth of OTM is consumed by chemical production, for example, for the manufacture of greases and second-rate oils, which are already of little use in technology and are also subject to disposal.
However, OTM is a type of high-calorie fuel, and it is advisable to use such a resource as much as possible on the ground for heat and power purposes, especially since modern technologies make it possible to burn it efficiently and environmentally friendly. Nowadays, there are no technical problems in the combustion of fuels: technology allows you to burn everything that burns and is difficult to burn. On the other side of the problem, we will consider how efficiently we burn these fuels and how useful we use this resource and the heat received from burning it. This material is for those who can count money and solve real problems.
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According to US experts, the annual consumption of motor oils alone in the world exceeds 42 million weight tons, i.e. about 60 million tons in conventional fuel. Of these, only a quarter (10-12 million weight tons) is reused, recycled or incinerated. Moreover, the produced oils, which we define as OTM, have a caloric content higher than coal, diesel and fuel oil and exceed 10,000 kcal / kg, which is a high fuel and energy value: annealing 3.4 kg of motor oil releases 34.6 kcal of heat. For comparison:
At the same time, 1 (one) liter of waste oil dispersed in the soil makes 100 to 1000 tons of groundwater unfit for drinking, which poses a serious danger. More than 40% of the surface of waterways in the world, according to environmentalists, is polluted and covered with a film of used motor oils. The danger of oils is not only in their toxic properties, but also in the ability to create a favorable environment for the accelerated reproduction of dangerous bacteria. In Russia in 2004, the consumption of lubricating oils approached 7.7 million weight tons, while only 1.7 million tons were collected, and about 15% (255 thousand tons) of them were regenerated, which is 3.3% of their general consumption. |
How to calculate pellet consumption
The calculation is carried out in several stages, although in general it is quite simple. Its result should be the average monthly fuel consumption of a pellet boiler during the heating season and the average cost of such heating. To do this, we will consider in parallel an example for a house of 100 m².
Stage one. First you need to understand how much heat actually enters the heating system when burning 1 kg of fuel pellets. After all, heating equipment is not so perfect as to direct all the energy received to heat the house, some of it still flies out into the chimney. To do this, the heat of burning pellets should be multiplied by the efficiency of the heat generator divided by 100:
5 kW/kg x 80% / 100 = 4 kW/kg.
Stage two. For the convenience of calculations, it is necessary to perform the reverse action in order to find out how many pellets need to be burned to obtain 1 kW of thermal energy in real conditions:
1 kW / 4 kW/kg = 0.25 kg.
Stage three.Since the weather outside changes during the heating season and the temperature fluctuates from +10 °C to -30 °C, the average specific heat consumption for the entire season for a dwelling of 100 m² will not be 10 kW, but half as much - 5 kW. Considering that power units are related to the time of 1 hour, the heat consumption per day will be:
5 kWh x 24 hours = 120 kW.
The same, only for a month:
120 kW x 30 days = 3600 kW.
Stage four. Now it is easy to calculate the consumption of pellets on average per month for a building of 100 m² during the entire heating season:
3600 kW x 0.25 kg/kW = 900 kg.
If the cold season lasts 7 months, as in Moscow, the Russian Federation, then the total number of fuel pellets for heating a private house with an area of 100 square meters will be 900 x 7 = 6.3 tons. In the same way, the average monthly consumption of pellets for a house with an area of 150 and 200 m² is determined, it is equal to 1.35 and 1.8 tons, respectively. Since the pellet is sold by weight and not by volume, it is not necessary to convert this amount into volume units.
Those who are interested in the theoretical value of the consumption of wood pellets on average per day can calculate it in this way (for our example):
120 kW x 0.25 kg/kW = 30 kg.
Attention! The average calculated value should not be confused with the actual fuel consumption on the coldest and warmest days. In a building of 100 m², it can vary between 15-60 kg of pellets per day
To get the approximate cost of pellet heating in monetary terms, you need to multiply the figures obtained by the price per ton accepted in your region. At the prices of the capitals of the Russian Federation and Ukraine, the monthly heating costs for a private house of 100 square meters will be:
- for Moscow: 0.9 t x 7000 rub/t = 6300 rub;
- for Kiev: 0.9 t x 2000 UAH/t = 1800 UAH.
It should be borne in mind that we carried out an abstract calculation and in the conditions of Ukraine the financial costs for pellet heating will be less due to the milder climate.
Pellets what is it
These are solid cylindrical granules 6-10 mm in diameter, obtained by pressing (granulation) of waste from various industries - woodworking and agricultural. Their use in the field of heat supply is very different from the combustion of other types of biomass - firewood, coal, sawdust and straw in its pure form.
The advantages of fuel pellets have made them one of the widely used energy carriers in Western Europe:
- high bulk density - 550-600 kg/m3, which saves space for fuel storage;
- low relative humidity, permissible maximum - 12%;
- due to the high degree of compaction and low humidity, the pellets are characterized by an increased calorific value - from 5 to 5.4 kW / kg;
- low ash content - from 0.5 to 3%, depending on the raw material.
The pellets have the size and solid structure to automate the combustion process, while the low ash content makes it last longer without intervention for maintenance.
Thermal equipment that burns pellets is stopped for cleaning from soot on average 1 time per week.
The fuel perfectly tolerates transportation and bulk storage, without collapsing or turning into dust. This allows you to arrange the supply of fuel to high-capacity industrial boilers from special storage facilities - silos, where a monthly supply of pellets is placed.
Fuel pellets are a convenient and environmentally friendly energy source that does not form dirt and dust when heating a private house, so it is gradually conquering the market of Ukraine and the Russian Federation.
Types of waste for the production of pellets
The raw materials for the manufacture of pellets are the following types of waste from various industries:
- wood chips, sawdust, slabs, wood chips and other substandard wood;
- husks remaining from the processing of sunflower or buckwheat seeds;
- stems of various agricultural crops in the form of straw;
- peat.
Environmental issues
Equipment manufacturers are silent about the problems of environmental protection in the process of OM combustion: harmful substances are released into the atmosphere. According to the world requirements of environmental standards, the content of harmful substances in gas emissions should be: dust - no more than 10 mg/m3, SO2 – 50, HСl – 10, HF – 1, CO – 50, NOX - 200, dioxins - 0.1 ng/m3. The content of heavy metal oxides should not exceed 3 mg/m3, including cadmium, mercury, lead - 0.1 mg/m3.
An analysis of modern OM combustion technologies reveals a number of environmental and economic shortcomings. In particular, fine dust (1–2 kg/m3 OM) and harmful gases are emitted into the atmosphere. The composition of highly dispersed fly ash includes mineral particles and unburned organic residues. Gaseous emissions consist of: carbon dioxide (CO2) and water vapor, heavy metal compounds, products of incomplete combustion, namely polyaromatic and halogenated hydrocarbons. Up to 7% of the mass of burned used motor oils is ash contaminated with heavy metals.
Thus, when disposing of OM, the following points should be taken into account:
- incineration is a highly technological complex process that requires multi-level treatment equipment due to increased sanitary standards;
- the need for preliminary settling after transportation, separation of sediment, water and antifreeze;
- high capital and operating costs for boiler equipment and air cleaning systems.
When burning 1 ton of OM, about 7 thousand m3 of flue gases are formed, which contain nitrogen and sulfur oxides, hydrogen chloride, polyaromatic hydrocarbons, chlorobenzene and heavy metals. The latter are sorbed by fly ash particles and on average contain: aluminum - 3.1 mg/m3; zinc - 2.7; lead - 1.6; copper - 0.15; chromium - 1.4.
Why are pellets good?
Comparison with other solid fuels
The strength of pellets is their progressiveness compared to wood, coal and even briquettes. Imagine a solid fuel boiler operating in the same mode as a gas boiler. Only even safer because pellets don't explode like natural gas.
The difference between gas and pellet heating is expressed in several points:
- the supply of pellets must be replenished;
- once a week the boiler stops for cleaning;
- during the operation of the pellet heat generator, the noise of pellets pouring down the plastic pipe is heard;
- the use of this fuel is not related to the work of utilities and various inspections;
- heating equipment that burns pellets is automated no worse than gas.
If we compare granulated waste with firewood or coal, then the latter win only in terms of cost.
In return, they take away comfort and time from the homeowner, as wood or coal heating requires constant attention. Even a long-burning boiler needs to be “feeded” 2 times a day and constantly cleaned, while a pellet one works non-stop for weeks.
The results of comparison according to other criteria also speak in favor of heating with pellets:
- Burning pellets is safer than wood and coal. Boilers equipped with pellet burners practically do not suffer from inertia, like conventional solid fuel ones. When the required coolant temperature is reached, the burner turns off and the fuel supply stops. Only a small handful of pellets burn out.
- The room with the pellet boiler is clean, there is no smell of smoke, which is present when the furnace is loaded with coal and firewood. Installation of a buffer tank is at the request of the owner. Pellet heat generators can do without a battery to dump excess heat.
Comparison in terms of technical characteristics and cost of different types of biomass fuel is presented in the table:
| Fuel | Heat output 1 kg, kW | kW Thermal plant efficiency, % | Real heat dissipation 1 kg | kW Price of 1 kg in Russia, rub | The price of 1 kg in Ukraine, UAH | Cost of 1 kW of heat in Russia, rub | Cost of 1 kW of heat in Ukraine, UAH | Ash content of fuel, % |
| Firewood freshly cut | 2 | 75 | 1,50 | 2,25 | 0,75 | 1,50 | 0,50 | 3 to 10 |
| Firewood dry moisture | 4,10 | 75 | 3,08 | 3,00 | 1,00 | 0,98 | 0,33 | up to 2 |
| Briquettes | 5,00 | 75 | 3,75 | 5,50 | 2,00 | 1,47 | 0,53 | until 3 |
| Agropellets | 5,00 | 80 | 4,00 | 7,00 | 2,00 | 1,75 | 0,50 | until 3 |
| Anthracite coal | 7,65 | 75 | 5,74 | 10,00 | 3,80 | 1,74 | 0,66 | from 15 to 25 |
The actual heat transfer of energy carriers may differ from the theoretical one and depends on the efficiency of your heating equipment and the moisture content of the raw materials you purchased.
Comparing the cost of a unit of heat on pellets, wood and coal, it is easy to conclude that pellet heating is not much more expensive than wood or coal heating.
It should be borne in mind that not the highest quality granules - agropellets - take part in the comparison. Pellets from wood waste show themselves even better.
Fuel briquettes have excellent performance in all criteria, but they lose to pellets in terms of the degree of automation of heating equipment.
Briquettes, like firewood, must be put into the firebox by the owner of the house. There are very few disadvantages of granular fuel:
- The high cost of boiler equipment and automation. The price of a medium quality pellet burner is comparable to a conventional solid fuel boiler with a power of up to 15 kW.
- Granules must be stored under certain conditions so that they do not become saturated with moisture and do not crumble. The method of storing a heap under a canopy is categorically not suitable, you will need a closed room or a container like a silo.
Fuel quality criteria
As you might guess, in order to release a significant amount of thermal energy, pellets must be of the appropriate quality. Unfortunately, given the ever-increasing popularity of this heating method, low-quality fuel samples from unscrupulous manufacturers or outright crooks began to appear on the market. Of course, the use of artisanal technologies does not allow for effective heat transfer. There is an erroneous opinion among many owners of pellet boilers that fuel consumption depends on the color of the pellets. This is not true at all. High-quality dark-colored pellets are made on the basis of wood fractions containing tree bark, light yellow pellets are made from furniture industry waste, and dark brown pellets are made from logging waste. High quality pellets have a fairly high density, the numerical value of which exceeds 1, so they must sink in water. Also, an important parameter that determines the quality of this type of solid fuel is the amount of ash remaining after complete combustion of pellets (ash content). According to the norms adopted in a number of European countries, this figure should not be more than 1.5%. In other words, after burning 10 kg of fuel, no more than 150 g of ash should remain. If this indicator is higher, a significant amount of slag will be formed during combustion. And this significantly reduces the performance of the boiler.
In addition to the characteristics described above, high quality pellets should have the following characteristics:
- The humidity of the pellets should not be more than 10%, otherwise the consumption of pellets will be significantly increased due to the need to compensate for the loss of heat capacity.
- The dust content must not exceed 11%. Exceeding this indicator is accompanied by an increase in ash content.
The packaging must be sealed. The most optimal option is when the granules go on sale in special bags with a waterproofing film on their inside. Such packaging allows the granules to retain their original quality characteristics for many years. Currently, 1 kg of fuel costs from 6 to 10 rubles. If a large bunker is used with the boiler, it is best to purchase fuel in large bags (big bags). The mass of one such bag is 900 kg.
Features of pellet heating systems
In order to evaluate the effectiveness of pellet heating, you need to know about the difference that exists between ordinary wood and pellets. During the manufacture of pellets, woodworking waste is used. Raw materials for the production of pellets or ordinary sawdust are first thoroughly dried, then steamed, as a result of which a viscous mass is formed, from which, under a pressure of 300 atmospheres, cylindrical granules with a length of about 70 mm and a diameter of 6 to 8 mm are formed. Boilers supplied to the market by pellet manufacturers equipment, from their counterparts that use ordinary firewood as fuel, are distinguished by a higher degree of heat transfer. Quantitative indicators of the heat of combustion of various types of solid fuels are shown in the table.
In addition to high heat transfer, pellet boilers have another advantage - their combustion chamber is loaded automatically. Automatic fuel supply is implemented as follows:
- A certain supply of pellets is stored in a special bunker made of stainless steel. The presence of a bunker of considerable volume allows you to refuel it with fuel at intervals of once every few days.
- Fuel enters the boiler through a flexible cable and an auger located inside it. Pellets by their own weight drive the auger into rotation, which ensures their supply to the distribution chamber of the boiler in the required quantity.
- Further, from the distribution chamber, the pellets enter the zone of the air burner, where they are incompletely burned, accompanied by the release of wood gas.
- The main source of high heat transfer is wood gas, which is completely burned in the afterburner.
Such a design of the boiler allows its owner, with continuous operation of the equipment, to fill the hopper with fuel only once every 3-4 days and remove solid combustion products, i.e. ash.
medium quality pellets
In the above calculations, the calorific value characteristic of high quality white granules, the so-called elite ones, was used. They are made from the waste of good wood and practically do not have foreign inclusions, such as tree bark. Meanwhile, various impurities increase the ash content of the fuel and reduce its calorific value, but the price per ton of such wood pellets is much lower than elite ones. By reducing the cost, many homeowners are trying to make their pellet heating more economical.
In addition to elite fuel pellets, cheaper pellets are produced from agricultural waste (usually from straw), whose color is somewhat darker. Their ash content is low, but the calorific value is reduced to 4 kW / kg, which will ultimately affect the amount consumed. In this case, the consumption per day for a house of 100 m2 will be 35 kg, and per month - as much as 1050 kg. The exception is pellets made from rapeseed straw, their calorific value is not worse than that of birch or coniferous pellets.
There are other pellets that are made from a wide variety of woodworking waste. They contain all sorts of impurities, including bark, from which malfunctions and even malfunctions occur in modern pellet boilers. Naturally, the unstable operation of the equipment always causes increased fuel consumption. Especially often heat generators with retort burners in the form of a bowl facing upwards are capricious from low-quality granules. There, the auger supplies fuel to the lower part of the "bowl", and around there are holes for the passage of air. Soot gets into them, due to which the intensity of combustion decreases.
In order to avoid such situations and the efficiency of the boiler does not decrease, it is advisable to choose fuel with a low ash content and in no case wet. Otherwise, problems with the screw feed will begin because the wet granules crumble and turn into dust that clogs the mechanism.It is possible to use cheaper fuel for heating a house with pellets when the boiler is equipped with a torch-type burner. Then the ash covers the walls of the furnace and falls down without falling back into the burner. The only condition is that the combustion chamber and burner elements will have to be serviced and cleaned more often, as they get dirty.
Calculation of feeder parameters
Spiral Feeder Performance n v rpm determined by the area of the working cavity and bulk density, the pitch of the spiral and the frequency of its rotation
,
where W – productivity of the spiral feeder, kg/h;
D - diameter of the burner body, m;
d - diameter of the blast pipe, m;
S - feeder spiral pitch, m;
n - rotation frequency, rpm;
is the bulk density of the fuel, kg/m3.
Having determined the rotational speed of the spiral feeder and based on the standard range of asynchronous electric motors, it is necessary to determine the gear ratio of the worm gear at the maximum load on the boiler unit, rpm
For the convenience of calculations and analysis, all calculations were performed in MS EXCEL.
Table 3.1 Calculation of burner parameters
|
Thermal power, kW |
Lower calorific value of wood pellets, kcal/kg |
Boiler unit efficiency |
Required fuel consumption kg/h |
Case diameter D, m |
Blast pipe diameter d, m |
|
750 |
4500 |
0,85 |
168,47 |
0,208 |
0,098 |
|
700 |
4500 |
0,85 |
157,24 |
0,208 |
0,098 |
|
600 |
4500 |
0,85 |
134,77 |
0,208 |
0,098 |
|
500 |
4500 |
0,85 |
112,31 |
0,208 |
0,098 |
|
400 |
4500 |
0,85 |
89,85 |
0,208 |
0,098 |
|
300 |
4500 |
0,85 |
67,39 |
0,208 |
0,098 |
|
200 |
4500 |
0,85 |
44,92 |
0,208 |
0,098 |
|
100 |
4500 |
0,85 |
22,46 |
0,208 |
0,098 |
|
0,085 |
650 |
0,5 |
3,85 |
195 |
750 |
|
0,085 |
650 |
0,5 |
3,59 |
195 |
700 |
|
0,085 |
650 |
0,5 |
3,08 |
195 |
600 |
|
0,085 |
650 |
0,5 |
2,56 |
195 |
500 |
|
0,085 |
650 |
0,5 |
2,05 |
195 |
400 |
|
0,085 |
650 |
0,5 |
1,54 |
195 |
300 |
|
0,085 |
650 |
0,5 |
1,03 |
195 |
200 |
|
0,085 |
650 |
0,5 |
0,51 |
195 |
100 |
Figure 3.1 Dependence of the main parameters of the burner on the load on the boiler unit
One of the main factors influencing the fuel consumption of solid fuel boiler units made of materials based on wood, and in particular in our case, these are pellets, is humidity. Humidity reduces the calorific value of wood-based fuel, which in turn leads to an increase in fuel consumption by the boiler unit.
The developed pellet burner must provide the necessary performance of the dosing unit of the screw feeder. The calculation results are presented in Table 3.2 and Figure 3.2.
Table 3.2 Calculation of the operating modes of the burner in case of a decrease in the calorific value of the fuel (increase in the moisture content of the pellets).
|
Thermal power, kW |
Lower calorific value of wood pellets, kcal/kg |
Boiler unit efficiency |
Required fuel consumption kg/h |
Case diameter D, m |
Blast pipe diameter d, m |
|
1 |
2 |
3 |
4 |
5 |
6 |
|
750 |
4500 |
0,85 |
168,47 |
0,208 |
0,098 |
|
750 |
4400 |
0,85 |
172,30 |
0,208 |
0,098 |
|
750 |
4300 |
0,85 |
176,30 |
0,208 |
0,098 |
|
750 |
4200 |
0,85 |
180,50 |
0,208 |
0,098 |
|
750 |
4100 |
0,85 |
184,90 |
0,208 |
0,098 |
|
feeder step, m |
Bulk density of fuel, kg/m3 |
feeder efficiency |
Feeder speed, rpm |
Gear ratio |
ED rotation frequency, rpm |
|
1 |
2 |
3 |
4 |
5 |
6 |
|
750 |
4000 |
0,85 |
189,53 |
0,208 |
0,098 |
|
750 |
3900 |
0,85 |
194,39 |
0,208 |
0,098 |
|
750 |
3800 |
0,85 |
199,50 |
0,208 |
0,098 |
|
0,085 |
650 |
0,5 |
4,03 |
195 |
785 |
|
0,085 |
650 |
0,5 |
4,12 |
195 |
804 |
|
0,085 |
650 |
0,5 |
4,22 |
195 |
823 |
|
0,085 |
650 |
0,5 |
4,33 |
195 |
844 |
|
0,085 |
650 |
0,5 |
4,44 |
195 |
865 |
|
0,085 |
650 |
0,5 |
4,56 |
195 |
888 |
Figure 3.2 Calculation results
As a result of the calculations performed, the optimal operating modes of the pellet burner were identified. In particular, with a gear ratio of a worm gear z = 195 to reach the rated heat output of the boiler, it is necessary to rotate the spiral conveyor with a speed of ntr = 3.85 rpm, respectively, the speed of the drive motor will be ned = 750 rpm
The regulation of the feeder performance with a decrease in the heat load must be done smoothly. This can be achieved by reducing the speed of the drive motor with a frequency converter.
In the event of a decrease in the calorific value of pellet fuel, it is necessary to slightly increase the rotational speed of the spiral feeder and, when operating at the rated heat load of the boiler unit, the rotational speed of the feeder can reach 4.5 - 5 rpm, and the frequency of rotation of the electric motor reaches 880 - 900 rpm Therefore, taking into account the operation on low quality fuel, it is necessary to choose an electric motor with a higher speed of rotation up to 1500 rpm
Pellets for home heating
Recently, many owners of private houses use compressed pellets made from waste from a wide variety of combustible materials to heat their homes. These granules are called pellets.Those homeowners who are just planning to install hot water boilers in their house that use pellets as fuel are interested in the consumption rates of this fuel material, as well as the amount of heat released during its combustion. We will try to cover these issues in as much detail as possible within this short article. As a rule, the choice of one or another type of solid fuel boilers is based on the availability and cost of fuel. In addition, many owners of private houses try to choose equipment that requires minimal maintenance. In other words, there is no need to fill the furnace daily, remove combustion products, etc. Therefore, among a wide range of types of solid fuel boilers, pellet equipment is most in demand.