- 1. Drying. The process of drying shall be a controlled process. Pyrogenetic processing of wood raw material is connected with its drying. The process of drying is almost always subdivided into two stages. The first stage is preliminary drying in dryers. The second stage is final drying during pyrolysis process.
Preliminary drying. The process flow depends significantly on the initial moisture content of wood. The larger is the moisture content the larger amount of heat is needed to accomplish the project, the longer is the duration of the process. The amount of heat application depends on the temperature difference and evaporation of moisture requires much energy. It is necessary to increase temperature of heat carrier and to increase time of drying. However during intensive drying the vapours tear wood and as a result, the charcoal is of poor quality, not solid, crumbling and undurable. As a rule, the pyrolysis process temperature is within 200… 220° C, maximum.
Until wood is not completely dry its temperature (under normal pressure) remains within the range of 100 ° C or a little higher. Change of relative humidity within 13-20 % is considered optimum and doesn’t affect the product yield. The first and the second stages are insured by proposed coal burning process.
- 2. Pyrolysis process control. Heating rate shall be maintained at each pyrolysis mode. Raw material shall be stored at a certain temperature for the required period of time, the final heating temperature shall also be maintained. Ris.10 (1) features temperature increase inside the device (retort) during heat application through the wall. So the figure shows to what temperature the retort shall be heated in order to obtain the required pyrolysis mode.
Ris.10 Temperature change during pyrolysis process. 1- Temperature outside retort. 2- Temperature inside retort. I- heating period; II- drying period; III – 1st stage of pyrolysis process; IV – exothermic stage; V- coal heating period.
The pyrolysis process is subdivided into four stages: 1. Drying (II). The temperature shall not exceed 150 °C. This is an endothermic process; 2. (III) Disintegration of hemicellulose, removal of part of chemically bonded water and formation of CO, CO2, methane, acetic acid, methanol. The temperature is within 150-275°C. This is an endothermic process; 3.(IV) disintegration of cellulose and lignin. Secondary reactions of polymerization. Formation of the main groups of resin. The temperature shall be within the range of 275...450 °C. This is an exothermic process. The process is especially complicated for control; 4. (V) Coal heating. Removal of volatile matters that are kept by means of adsorption from carbonic framework. Formation of carbon crystalloid structures. Detachment of functional groups held by carbon. Endothermic and exothermic reactions go parallel. Total balance is endothermic. Coal heated up to 500° is not pure carbon. Should the temperature of charcoal heating be increased up to 600 ° C in this case emission of carbohydrates (methane, ethane, ethylene, etc) will take place.
At temperature range within 700-950°C emissions of hydrogen will take place mostly. The majority of consumers consider that high quality charcoal is coal heated up to 450… 550 °C. In case of high-speed pyrolysis yield of charcoal is by 30…50 % lower than in case when coal is subjected to heating in hot zone for a longer period. In case of oxidizing pyrolysis (with additives of oxygen) also reduces charcoal yield but improves its quality as raw material for activated charcoal production and for some other applications. If we regard wood material as a whole we may note that the heating rate in ordinary retorts with external heating is specified by emission and heat-transfer speed from heat carrier through the wall due to heat conductivity and inside the retort by heat convection from the wall to wood (1).
Charcoal quality and yield depends on proper fulfillment of the first two items.
- 3. The requirement of using heat from charcoal while it is being cooled.
- 4. Optimal use of radiated energy.
- 5. The whole process shall correspond to the laws of nature. In this case it will be natural and optimal.
- 6. Meeting of ecological, fire safety, accident prevention and labour protection requirements.
In order to better understand charcoal burning unit let’s view some of the basic moments.
Diagram, Fig. A1.2.3, features a bell. Let’ s call it “heat–accumulating bell”, if it is provided with an exit for fume gases exhaust directly into the pipe or through the next standing bell in gas flow direction through “environment” having a discharge zone (-P).
The form of the bell as well as its volume may be different. For example, it can be round, rectangular, it can have a ã-form or it may be cruciform, etc. It may be provided with any heat consumer (water or air boiler, etc) or heat source or consumer and heat source together. The diagram contains the following designations: Letters D and T denote blast into and draft from the bell respectively. Blast creates an “environment” with excess pressure marked by “+P” and draft - an environment with vacuum marked as “-P”. Blast and draft are applied to points of inlet and outlet from bell 1 and 2. Hot gases carry heat energy and products of combustion. We are interested in heat energy transfer; therefore it is considered that electric heater is a source of heat marked by the letter “C”. In this case it is not needed to exhaust the products of combustion.
If we supply a certain amount of air into the bell in a unit of time through point 1 and remove the same amount of air from point 2 in a unit of time (when the temperature inside and outside the bell is equal), in this case pressure in the bell won’t change. That is, if blast D and draft T are equal than pressure in the bell remains without change. If hot gases are supplied into the bell from a certain environment temperature and pressure inside the bell will increase. Hot gases give up their heat to the bell walls and to the consumer located inside it. Fig. A1 features this case. As the temperature increases gravitational head (pressure) arises in the bell. At this moment temperature and pressure in each upper section increases. This increased pressure appears over the whole height of the bell.
If we install an electric heater into the bell, even in case of insignificant excess of draft over blast temperature and pressure will increase in each upper section. Hot gases after they have given up their heat to the bell walls and to heat consumer located in it, flow to discharge zone created by the draft. Excess pressure is created over the whole height of the bell. Such a case is shown in Fig. A2.
Let’s view the condition of the system if we install an electric heater into the bell when the draft is significantly larger as compared with the blast, Fig. A3. Two forces specifying the condition of the system act on gas flow. These are pipe draft (natural or artificial) and gravitational (temperature) head. Pipe draft impact (depression) is getting low in each upper section, while temperature head increases. In the lower level of the bell the total pressure creates depression, which is specified by the preset values of pipe draft and temperature. On a certain height these two forces become equal and there will be no depression. Above this level high pressure is formed in the bell. The temperature will increase in each section, which is located higher. Hot gases heat the bell’s walls and heat consumer located inside and then flow to depression zone created by the draft.
Let’s view the bell shown in Fig. B 1.2.3.Let’s call it ”bell-type furnace”, hereinafter referred to as the furnace. If the furnace is not provided with exhaust of hot gases directly into the pipe then the gases are exhaust through the heat-accumulating bell shown in Fig.A3, that is through “environment” having depression (-P).The form of the furnace as well as its volume may be different. For example, it can be round, rectangular, etc. It may have any heat consumer inside (retort for pyrolysis of wood at drying stage, etc) or source of heat (retort at the working stage or at cooling stage, etc).
If the furnace has no heat consumer or is provided with it then vacuum is created inside it. Such condition of bell-type furnace is shown in Fig. B1.
If the furnace is provided with a generator (a source) of heat high pressure is formed inside it and the so-called cool, exhaust gases flow from it into heat-accumulating bell, that is in “environment” having a depressurized zone. Temperature and pressure in the furnace will increase in each upper section. Such state of the system is shown in the drawing, Fig.B2. If in this case from the side of point 1 there is “environment” with atmospheric pressure (P) then hot gases will flow towards point 2, into the “environment” containing vacuum. Such state of the system is shown in Fig. B3.
In order to solve technological tasks set forth during charcoal burning we propose to use the unit built in accordance with the formula: The unit consists of a number of bell-type furnaces, each of them being surrounded be a heat-accumulating bell, which in its bottom part contains free gates to connect them with each other. The upper part incorporates channels for interconnection of bell-type furnaces and heat-accumulating bell. The channels are provided with gates, Fig. C. The diagram has the following indications: 1-8- bell-type furnaces (furnaces) with convectors; F- heat-accumulating bell (in all the other diagrams marked by number 5). Pipes for delivery of gas-vapour mixture-8 to fire box of the heat-accumulating bell-11 for burning.Fire box –11 of the heat-accumulating bell. Connecting channel –14 located between retorts and heat-accumulating bell. Connecting channel –14 between retorts and heat-accumulating bell with a gate. The accumulated heat from heat-accumulating bell may be used for wood drying or be delivered to any furnace or used for other purposes as well. Such a design makes it possible to get high temperature in the furnace and enlarge the limit of adjustment of pyrolysis temperature. The unit may be started through any furnace, using wood as fuel. Combustion catalyst as per the height is included in the combustion chamber of the retort. It is needed for stabilization of wood burning during start-up and also for stabilization of combustion of vapour and gas mixture in operation mode. Air supply for combustion of gas is supplied through the ash-pit door or heat exchanger of regenerator. The whole process may run automatically. The pipe may have any location, as shown in Fig. C, depending on the crane equipment available.
Such design of the unit ensures flexibility of charcoal burning process due to flow transfer of hot gases and vapour and gas mixture as well as ombustion capacity adjustment in the furnace (retort heating degree). Such a method provides a possibility of using process cycle (time periods) delay individually in each retort. So we have a certain sequence. For example, an initial pyrolysis period takes place in retort 1; final pyrolysis period takes place in retort 3; cooling of finished coal takes place in retort 4. In retort 2 (and as a variant also in retort 6) charging and preliminary drying of fuel takes place. Other variants of process cycle change are also possible. It shall be pointed out that the unit possesses all remarkable features of the “free gas movement system”. These features are viewed in the articles “Once again about the system of free gas movement” ; “Pyrolysis of biological fuel in the bell and combustion of its products in the system of free gas movement. The system with forced gas movement doesn’t possess any of these features.
The furnace of each retort, independent furnace with an ash-pit, fire box door, fire-grate, fire box and combustion catalyst made of fire resistance grate brick. Each furnace is separated from another one by heat-accumulating bell.
Fig. D features cross-section over the retorts of furnaces No.1 and No.2 , Fig. C in the diagram. There are the following designations in Fig. D: bell-type furnace-1, pipe-2, used to deliver vapor and gas mixture into combustion chamber (6). Detachable (removable) retort-3. Removable grating-type cylinder – 4, for wood subjected to pyrolysis process, with seal cover for retort (-3). Cover is made separately from the grating-type cylinder. Heat-accumulating bell-5 (F). Combustion chamber-6 (3). Fire box for wood -7. Pipe-8 to deliver excess amount of gas and vapour mixture into the fire box of heat-accumulating bell for combustion.
Adjustable grate in closed condition-9. Adjustable grate in open condition -10. Fire box of heat accumulating bell -11 (block made of several pipes-8 with burners). Combustion of vapour and gas mixture takes place through one of the burners at each period of time. During any period of process cycle self-ignition of vapour and gas mixture takes place as soon as it is exhausted from any retort.
In accordance with technology pyrolysis of wood is foreseen in retort with external heating. Heating of fuel inside retort takes place due to convective heat exchange, therefore retort shall be heated from the bottom and in the lower part of the side surface. In connection with this a combustion chamber-6 is installed in the lower part of retort -3, with an exit from fire box for wood and nozzles through which gas received during pyrolysis process is delivered. Air necessary for combustion is also supplied to this chamber (a variant with regeneration technology is also possible). The proposed design of retort and furnace ensures that these requirements are met. The upper part of retort incorporates pipe with gate –10 through which excessive gas is exhausted (when adjusting combustion capacity) to be combusted in the fire box of heat-accumulating bell –11. The fire box is designed in accordance with the formula.
“The stove’s lower level and the fire box are combined to form a single space creating a lower bell”. Pressure is created in retort during pyrolysis process. The combustion capacity (retort heating) is adjusted by means of pressure change in retort by means of gate opening (possibly in automatic mode). Transfer of ways of vapour and gas mixture takes place. A variant of ways and volume of vapour and gas mixture transfer is possible by means of installation of three-way gate, which delivers the required amount of vapour and gas mixture in the required direction. The exhaust of gases takes place in the lower part. Exhaust gases are delivered into heat-accumulating bell in conformity with the diagram shown in Fig. B2.
At the IV-th stage of exothermic reaction when the charcoal temperature exceeds the preset permissible value temperature adjustment (its decrease) in the furnace is carried out due to transfer of hot gas flows used for drying. The excess amount of hot gases is delivered to heat-accumulating bell or into the furnace, in which the temperature has to be increased, through the gate.
Charging of wood, charcoal discharge.
Wood is charged into a removable grating-type cylinder- 4 manually or by means of wood-chopper conveyer. After that it is put into one of retorts for preliminary drying - by means of crane. Charcoal already cooled is discharged in grating-type cylinder-4 or retort-3 by means of crane and is supplied into bin for processing, dozing scales and sacks. With retort-3 removed from the furnace opening in the furnace may not be closed at once as there is a small draft directed downwards. Atmospheric air comes to heat-accumulating bell, and flows down cooling it a little bit (gas damper effect). Exhausted hot gases from the heat-accumulating bell are exhausted into the depressurized “ Environment”, that is into the pipe. The system functions in accordance with the diagram shown in Fig. B3.
Preliminary drying. Using heat of charcoal being cooled
Let’s view the drying diagram shown in Fig. D. The diagram has the following designations:
2- furnace with retort during drying; 4- furnace with hot retort being cooled; 11- fire box; 12 and 13- cover in open and closed state respectfully; 14- connecting channel between retorts and heat-accumulating bell; 15- four positions gate ensuring hot gas passing between retorts, and from heat-accumulating bell –5 into one of retorts. The upper gate is used for blowing the furnace into the atmosphere in mode of bringing coal to temperature at which its discharge is allowed. 8- pipe to deliver vapour and gas mixture into furnace fire box.
The operation principle is as follows. In grating-type cylinder-4 wood is put in retort-3 of furnace “2”. Seal cover –12 of retort is slightly open. Drying process can be carried out in accordance with two variants. For example, as per Fig. D:
- 1. Hot gases from hot retort are delivered (natural circulation) from furnace “4” to furnace “2” through channel-14. At this moment the passages from heat-accumulating bell into the channel and the upper one into the atmosphere are closed by means of gate.
- 2. Hot gases are delivered from heat-accumulating bell into furnace “2” through open gate to channel-14. In this case channel running towards furnace “4” and exhaust hole into the atmosphere are closed by means of gate. Fuel in retort of furnace No. “2” is dried in a similar way as water is evaporated from the pan on the stove. The drying temperature is adjusted by the value of gate opening.
The process of charcoal cooling is considered finished when its temperature reaches 45-50 ° C. Lowering of charcoal temperature at the end of the process is achieved by blowing cold air through open ash-pit door of the furnace, with the top gate and opening into channel 14 being open. All the other gates remain closed.
The technological process permits that at various process cycles the temperature in each furnace may differ from the temperature in heat-accumulating bell significantly. For example, at pyrolysis stage and charcoal heating the temperature has its maximum value and at the initial stage of drying or at the end of retort cooling with charcoal it has the minimum value. Besides the process technology requires quick change of temperature mode in the furnace depending on the furnace stage. In other words, the system shall not be an inertial one. The energy produced shall remain in the heat-accumulating bell in maximum volume. Therefore the walls of charcoal burning unit shall be made in such a way that these conditions be fulfilled.
The walls between the furnace and heat-accumulating bell shall be made as three-layer walls in the following design:
From the furnace side the material with high thermal conductivity shall be used so as it would be possible to decrease or to increase quickly the temperature inside the furnace that is required at various stages of charcoal burning.
From the side of heat-accumulating bell the material with high heat-accumulating capability shall be used.
From the outside it is necessary to use the material protecting the unit from the atmospheric attack. The middle layer of mineral thermal insulation shall ensure protection against heat transfer from the heat-accumulating bell into the furnace and from the side overlooking the street –protection of heat transfer into the street.
The wall separating heat - accumulating bell and the street shall also be made as three-layer wall. The inner layer shall be made of material with high heat -accumulating capability. The external layer shall be made of material protecting from the atmospheric attack. The middle layer of thermal insulation shall ensure protection against heat transfer from the heat-accumulating bell into the street.
The formula ”The unit consists of a number of bell-type furnaces, each of them being surrounded by heat-accumulating bell, which in its bottom level contains free gates to connect them with each other. The upper part incorporates channels for interconnection of bell-type furnaces and heat-accumulating bell. The channels are provided with gates” describes method that may be used not only for creation of unit to produce charcoal. It can also be used to create heating boilers used for burning of cardboard boxes, wooden cases and other debris in shops, markets, etc. and also to process waste of timber industry, peat-cutting and waste processing, etc.
I am already an old-aged man and I have no time and opportunity to patent my works, neither do I want to conceal the results of my works. Many people from all over the world address to me and express their gratitude for assistance and help. Some of them asking to sell the drawings of furnaces and boilers. Selling of drawings and similar job require much time and certain experience, which I do not have and which I don’t need. It’s a pity that I physically am not in a position to publish enormous material I have and make it the common property of people. I have no opportunity to finance and carry out tests and revision of our systems and solve the questions laid out in section “Proposals for research”. As a result of this work we may have some significant discoveries. Summing up the above-mentioned, I declare the above formula as priority application for invention of method for creation of energy installations, property of world community. Those who wish to use the results of this work shall obtain the right in accordance with established procedure and effect payment to the international fund. The fund shall be governed and the assets shall be distributed under the control of international organization and shall be spent for the development of ”Free gas movement system”. The main task of those people who will receive assets from the fund is to make the results of their work known to all people.
References:
I.Kuznetsov, Russia, 02.2005 voice: (343) 3077303 e-mail: igor@stove.ru http://stove.ru
27/02/2005 © Igor Kuznetsov "Kuznetsov's stoves"
