JPS5864408A - Combustion method of fossil fuel utilizing waste heat - Google Patents

Abstract

PURPOSE:To recover waste heat in the form of hydrogen fuel and conseqently contrive to economize fuel by a method wherein a part of the waste heat is converted by means of a thermo-electric element system into electric power, which electrolyzes the cooling water of the thermo-electric element system into hydrogen used for multi- fuel firing. CONSTITUTION:In order to apply the titled combustion method to a conventional kerosene burner, a plurality of sets of the thermo-electric element system 5 comprising in connecting, for example, thirty two pairs of cylindrical p-n junction thermo- electric element (Bi-Te type alloy) pairs in series are installed onto the vessel wall 2 forming the side surface of a combustion tube 1. A cooling water pipe 8 consisting of a cooling water system 7 is fitted to the heat radiating part 6 of the thermo-electric element system 5 in order to feed cooling water W by means of a pump 9. An electrolysis system 10, in which high temperature water is electrolyzed for generating hydrogen and oxygen by employing the DC current produced at the thermo-electric element system 5 as electric source of electrolysis, is provided at the lower part of the combustion tube 1. Furthermore, said hydrogen is led through a means 13 for preventing a reversed flow to the combustion tube 1 and as well a said oxygen is sent together with fuel through a supply pipe 3 in the combustion tube 1 to be fired mixedly.

Description

[Detailed Description of the Invention] The present invention provides a method for burning fossil fuels such as kerosene and natural gas.
This invention relates to a combustion method that generates hydrogen using waste heat and co-combusts it with fuel.

Generally, natural gas, liquefied petroleum gas, and kerosene 1 heavy oil.

In fossil fuel combustors using pulverized coal, waste heat is unavoidable for purposes other than heating. In all of the large, medium, and small combustors that are currently in widespread use, waste heat is equivalent to 20% to 30% of the calories in the fuel that should be used effectively, and that amount of fuel is wasted. . Therefore, although the use of this waste heat has been considered, there is no effective method yet.

In particular, it is said that it is difficult to utilize the heat released from the side of one combustor.

On the other hand, the price of fluid fossil fuels such as petroleum is on the rise, and it is necessary to completely burn them and adopt combustion methods that utilize heat to increase efficiency. However, in the conventional combustion of this type of fuel, complete combustion is not achieved, and combustible substances such as coal particles, carbon oxide, and hydrocarbons are emitted into the waste gas, which wastes fuel and , contributing to air pollution.

The present invention was made in view of the above circumstances, and its purpose is to convert a part of waste heat into electric power using a thermoelectric element system, and to electrolyze the cooling water of the thermoelectric element system using the electric power. An object of the present invention is to provide a fossil fuel combustion method that can save fuel by recovering waste heat in the form of hydrogen fuel by generating hydrogen and co-combusting it with fuel.

Another object of the present invention is to co-fire hydrogen by co-firing hydrogen;
To provide a combustion method that efficiently utilizes fuel by increasing the combustion temperature and completely burning the fuel.

In order to achieve such an object, the present invention uses a thermoelectric element system installed at an appropriate location on the vessel wall of a fossil fuel combustor to generate DC power from the waste heat from the nuclear vessel wall, and (b ) A cooling water system attached to the heat dissipation part of the thermoelectric element system and driven using a part of the DC power generates high-temperature water or water vapor, and (C) Add the water or steam from Akanetan to the above (
a) A part of the electric power obtained in the IC is used for electrolysis to generate hydrogen and oxygen, and (d) the hydrogen is guided to the combustor and co-combusted with the fossil fuel. .

Hereinafter, the configuration of the present invention will be explained in detail.

First, by generating DC power from waste heat, high-temperature water is obtained.

The above-described DC power is generated by attaching a semiconductor thermal lightning element having a pn junction to an appropriate location on the wall of the combustor, for example, on the side wall. Many semiconductors for thermoelectric elements are known, such as Ge.
-8i alloy system (trivalent metal such as In for p-type, F for n-type)
There are pentavalent metals such as isb (power rl), B1-Te alloys (Sb for p-type + Se added for "type"), etc.

One pair of thermoelectric elements generates about 1 mV of DC power at a temperature difference of 60°C, so for example, one unit of 32
By connecting the pairs in series, a voltage of approximately 2V can be generated.

The reason why such a voltage is required is that K to electrolyze water at normal temperature and pressure is theoretically required to be 1.23 V, but in reality, about 1.8 V is required due to overvoltage.

A plurality of these thermoelectric element units are installed on the side wall depending on the size of the combustor. For example, one of them is dedicated to a small motor that drives a cooling water pump, and the power from the other units is used as a power source for electrolysis. shall be.

The number of thermoelectric element units, the number of thermoelectric elements constituting the unit, etc. can be appropriately set depending on the force of the motor, the current, the required power for electrolysis, etc.

Furthermore, since thermoelectric elements and polycrystals can be manufactured in large quantities and at low cost using sintering methods, they do not have the disadvantage of being too expensive to manufacture single crystals like silicon solar cells, and can be manufactured using L or 4 amorphous silicon p-rls. If.

Since there is no such instability, it is suitable for use in waste heat utilization.

The temperature on the high temperature side (p-n junction) of the thermoelectric element system is at least 20
0℃, the temperature on the low temperature side is assumed to be at least 100℃,
In reality, the temperature will be much higher than this.

At this time, the low temperature side is cooled with cooling water to maintain the temperature difference in the thermoelectric element system at 70° C. or higher. That is, cooling water is supplied to the heat radiating section (low temperature @) of the thermoelectric element system to cool it, and the cooling water is made into high temperature water in the heat radiating section. The temperature of the cooling water will be around xorfc. This cooling water is supplied by a cooling water system equipped with a small motor and a cooling water pump that are driven by part of the electric power of the thermoelectric element system described above.

Next, the above-mentioned high-temperature water is electrolyzed using the electric power obtained by the above-mentioned thermoelectric element system to generate hydrogen and oxygen. This is the energy W required for water electrolysis
This is because d can be small if the thermal energy Qd of water is large, as expressed by the following equation.

Wd=Hd-Qd ・・・・・・・・・・・・・・・
・・・・・・(1) That is, Hd#i is the total energy required to decompose water, and it is constant at 68.3 Kd/mol, so if the temperature rises, the thermal energy of water Qd This is because the electric energy Wd required for decomposition becomes smaller.

The hydrogen produced by the electrolysis is introduced into a fossil fuel combustor and co-combusted with the fossil fuel.

This makes it possible to use hydrogen as fuel. Note that the simultaneously generated bulk can be introduced into the combustor separately from the hydrogen to contribute to the combustion of the fuel. The reason for introducing hydrogen and oxygen separately is from safety considerations.

Next, the extent to which waste heat is utilized in the present invention will be explained.

Let the total amount of waste heat be QO, and let its temperature be Th.

Only ηte Q6 of the QO is converted into electric power by the thermoelectric element system, and most of the remaining (I-ηte)Qo is used to heat the cooling water. If the heating efficiency is ηW, then the heat used to heat the water and make it high-temperature water at temperature Tc is ηW(1-ηte)
It is Qo.

On the other hand, if the efficiency of water electrolysis is ηet, then ηet = Jin...
・・・・・・・・・Defined by (2). Here Q
O is the amount of heat generated when hydrogen of 1 mO4 and # of 1/2 mat combine through a combustion reaction, and n is the number of moles of hydrogen produced by electrolysis.

Organizing the above process from the perspective of the law of conservation of energy, assuming that ``oQo'' out of the total waste heat is effectively used, ηoQo=ηet''teQo+ηw (1-ηte)
Qo -----= +31. From this, the total efficiency of this device is ri0−ηel−1te+ηw(1−ηte
)・1 fist...White...(4), Wd=ηte
Substituting QO and equation (2) into equation (3), On ηo -=-,, -ten'7w (1-'7te)...
・・・・・・・・・・・・・・・＋51 and Cao〈It is also possible.

Note that the power generation efficiency of one pair of thermoelectric elements is approximated by the following formula. 2Fi is the thermoelectric performance water number of this thermoelectric element pair. In the inventor's experiment, 2×1O-3' in Z
c-1r Th 593, Tc Ki 387, ηte
=6.7N. In reality, it appears to be 5%t1.

What is the electrolysis efficiency? et-80X, water vapor generation efficiency ηW=7O
If we estimate N, then η0 = 70 at most according to equation (4).
67N. In reality, it is expected to be in the 6ON range, but even if the waste heat is 3ON, which is the calorific value of the fuel, 18% of fuel can be saved.

Thus, according to the present invention, 20% to 30% of the calorific value of the fuel
Approximately 60% to 70% of the waste heat generated can be recovered as water, which can save fuel, but it is possible to further save fuel by adding this hydrogen and co-combusting it. can.

That is, by adding hydrogen and co-firing, the temperature of the flame increases by an average of 17 N, improving the efficiency of the heat exchanger connected to the combustor. Since the heat transfer rate is proportional to the temperature gradient, the rate of increase in transferred heat is equal to the rate of increase in temperature. This can be considered as a reduction in fuel savings, so if you add it up with the effects mentioned above, the fuel savings will be as much as 30%. In addition, by adding hydrogen, complete combustion of the fuel becomes possible, which helps to fully utilize the calories of the fuel, and also reduces soot and smoke due to the complete combustion of the furnace material, making it easier to clean the combustor. This eliminates the need for maintenance, and also extends the life of the combustor. Moreover, air pollution can be reduced.

Next, an example of a combustor used to carry out the combustion method of the present invention will be explained with reference to the drawings.

FIG. 1 is a configuration diagram showing an example of a combustor used in the combustion method of the present invention. The combustor shown in the figure is applied to a normal kerosene combustor, and includes a combustion tube 1, a thermoelectric element system 5, a cooling water ice 7, and an electrolysis system 10. Note that the fuel inflow route is omitted in the figure for the sake of simplicity.

The thermoelectric element system 5 has a cylindrical shape with a diameter of 5 cm and a length of 7 cm.
It is constructed by connecting 32 pairs of n-junction thermoelectric elements (Bi-Te alloy) in series, and a plurality of sets are mounted on the chamber wall 2 on the side surface of the combustion tube 1. A cooling pipe 8 is attached to the heat radiation section 6 of this thermoelectric element system 5, and cooling water W is sent by a cooling water pump 9. The cooling pipe 8, the pump 9, and a small motor (not shown) constitute a cooling water system 7, which converts cooling water into high-temperature water. This small motor is driven by DC power from the thermoelectric element system 5.

An electrolysis system 10 is provided in the lower part of the combustion tube 1, and uses the DC power of the thermoelectric element system 5 as a power source to electrolyze the high-temperature water. Connected to this electrolysis system 10 are conduits 11 and 12 that conduct hydrogen and oxygen, respectively. The conduit 11 leads hydrogen to the combustion tube l via the backflow prevention device 13. conduit 12
is connected to the fuel supply pipe 3, although the connection part is not shown, and sends oxygen into the combustion cylinder 1 together with fuel. Note that the figure shows a 4Fi ignition device.

To give an example of the operating conditions of this combustor, under normal best combustion conditions, the average temperature of the flame was 1033°C, and the temperature of the side wall of the combustor was 688°C. The temperature of the high-temperature water produced when the cooling water was heated was approximately 100°C. And the electrolytic voltage is 1.51V or 61.38V
It changed with time, but the best steady state value was 1.47.
It was V. This is done by electrolysis of water at room temperature.
This corresponds to power saving of N.

Next, typical examples of the present invention will be shown.

Example [1] The amount of kerosene is controlled so that it burns at a rate of 120 C per second. This corresponds to a heat radiation amount of 1100 jK per second. At this time, we used 5 pairs of thermoelectric element systems with an output of 2 V, and used the 5 pairs in parallel to obtain a current of strong IA. The current density of the element is 1.2A
/d. 1.47V.

Water at 100° C. was continuously electrolyzed with the output of the IA, and the amount of hydrogen collected during 2 hours was measured and found to be 5.61.

Example [2] Kerosene was burned while maintaining the combustion amount at 12 cc/sec, and hydrogen and oxygen were generated by electrolysis in the same manner as in Example [1] above. When we repeated the experiment of co-firing these with kerosene, we obtained the following results.

Due to co-firing, the color and brightness of the first K flame decreased, and secondly, the flame temperature increased from 1033℃ before co-firing to an average temperature of 1208℃.
rose to Thirdly, the amount of soot and smoke collected by the glass plate during the flame was 1.6 in the non-co-fired state for 5 minutes after ignition, and 0 during the steady combustion.

In Examples (1) and (2), a backflow prevention device was installed in the middle of the conduit that led hydrogen to the combustion cylinder. This valve is designed so that the valve closes when the flow rate of the hydrogen being sent becomes less than 81 V'S. This safety device never worked during the experiment in this example.

Through experiments, it was predicted that there would be an optimal mixing ratio of fuel and hydrogen under conditions specific to the combustor and fuel, and Examples (]) and [:2) are close to that condition.

However, it was not possible to clarify the theoretical busyness ratio.

In the above description, a case has been described in which high-temperature water is electrolyzed, but a configuration may also be adopted in which water vapor is generated and this is electrolyzed. In water vapor electrolysis, the distance between the electrodes is small,
A specially designed electrolytic cell with concentric cylindrical electrodes is used.

As explained above, the present invention uses waste heat to obtain DC power, generates hydrogen through electrolysis using this as a power source, and recovers the waste heat in the form of hydrogen fuel. By co-firing hydrogen, the combustion temperature increases and complete combustion results in efficient use of heat and complete use of fuel calories, and also has the effect of purifying waste gas.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a combustor used to carry out the combustion method of the present invention. 1... Combustion tube 2... Vessel wall 5... Thermoelectric element system 7... Cooling water system 10... Electrolysis system applicant
Miura-shi Diagram 1 Procedural Amendment (Saba) December 4, 1980 Dear Commissioner of the Japan Patent Office 1, Indication of Case Patent Application No. 163946 1982, Title of Invention Combustion of fossil fuels using waste heat Method 3: Relationship with the case of the person making the amendment Patent applicant office
762 Oisone-cho, Kohoku-ku, Yokohama-shi, Kanagawa Prefecture Name (full name)
Miura-shi4, agent 〒107 telephone 586
-9287 No. 6, subject of amendment (1) In the first line of Example [1] on page 13 of the letter, ``12 ccJ per second is corrected to 1.2 CeJ per second◇ (2) In the second line of the same, `` Correct 11000&l J per second to ``110000al J per second〇 (3) Correct ``12ce/sec'' to ``1.2Cc/sec'' in the first line of Example [2] on the same page ◎ That's all.

Claims (1)

[Scope of Claims] m(a) A thermoelectric element system installed in an appropriate position on the vessel wall of a fossil fuel combustor to generate DC power from waste heat from the vessel wall, and Φ) The above thermoelectric element system A cooling water system that is attached to the heat dissipation part of and driven using a part of the DC power generates high-temperature water or steam, (C) and (B) above.
The high temperature water or steam obtained in (a) is electrolyzed using a portion of the electric power obtained in (a) above to generate hydrogen and oxygen, and (d) the hydrogen is guided to the combustor and the A method of burning fossil fuels using waste heat, which is characterized by co-combustion with fossil fuels. (2) The method for combustion of fossil fuel using waste heat according to item 1, wherein the hydrogen and oxygen obtained in the above (C) are separately guided to the combustion 5 and co-fired with the fossil fuel.