;
Theme "Modification elements of the gas fuel combustion control system for its optimization of economic efficiency "
Analysis of the present researches
General outline. In the Ukrainian economy energy conservation and energy saving
technologies are of primary implementation into the industry. Thereby, an important role plays detail and complex
studies of heat and power resources and systems. Heat energy is an indispensable condition of human beings, society
improvement, which one lives in, and provision of the humans’ everyday life. Industry systems optimization of heat energy
production and discharge, adjustment of energy and water balances, energy saving and audit allow to improve heat and
energy development perspectives, to raise technical and economic indexes of heat and energy equipment.
Efficiency, safety, security and economic efficiency of the heat and energy equipment of the
boiler plants are determined mostly by the way of the fuel burns, perfection and efficiency of the choice of devices and equipment.
The improvement of reliability and efficiency of heat supply depends on the work of the heat boilers, rationally projected heat scheme
of the boiler room and wide implementation of the energy saving technologies, the fuel saving, heat and electric power.
To date, the gas problem in the world makes to reconsider the process of the fuel burning and improve
the technologies for the coefficient of performance raise under the conditions of the reduction of the fuel resources expense. Modern
science and industry technologies presuppose the use of the high temperature reactions to supply the heat system with the power source.
The effectiveness of the power sources in the given terms (fro example the use of the gas mixture in the torch, in particular) should provide
the maximum temperature and the efficiency of the fuel combustion.
Analysis of the present researches. Several papers are devoted to the problem connected with the heat and technical processes.
For example, in the paper [3] the dependence of the water heating from the amount of the fuel supplied are taken into account. The
researchers in terms of the optimal torch parameters for the water heating have been done. Rest on the achieved mathematical model of
the heated up air heat exchange inside the combustion chamber with the convection surfaces of the heating[2], the theoretical data of the
torch temperature in the different points of the environment are achieved. In this works is shown the following; the achievement of the
maximum temperature for the particular burner is possible in terms of the oxidant and fuel optimal proportion supplied. The mixture of
the components takes place in the working medium of the burner so that the prepared mixture of the initial components enter the torch (burner)
nozzle. The received flame over the taking away from the nozzle is constant and axially symmetric. It allows us to use heat and power methods
of the temperature determination. Nevertheless, these researches don’t touch upon the metrical matter and don’t make an accent on the choice
of the transducers, which can be used in the aggressive high temperature medium with the less possible error.
Problem specification.
Built up the mathematical model of the water heating form the fuel supplied to the system entrance, that will help to make the process more
economically efficient due to the increase of the coefficient of performance of the boiler plant work. For this purpose it is necessary to make
a study of the optimal parameters of the torch in the different points of the environment inside the burning chamber with the convectional surfaces
of the heating. Take into account, that the torch is evenly spread inside the burning chamber, as the type of the burner is diffusive, that is the fuel
is mixed up before the entrance to the burner.
Relevanceof the researches fulfilled in the present paper runs as follows; for the optimal arrangement of the combustion process and, therefore,
effective use of gas, it is necessary to study the structures of the flame torch of the burner being used. [2]
Problem solution. Burning chamber represents an enclosed space with one in and out, into which the heat enters,
and the smoke exhauster removes the end product of fuel combustion/
Figure 1 - Structural scheme of burning chamber
The structural scheme of burning chamber has a look shown at the figure 1:
1 – burning chamber; 2 –burner unit; 3 – drum;4 – vapour superheater;5 – steam cooler;6 – vapour superheater outlet chamber;
7 – remote cyclone collector; 8,9 – water economizers; 10,11 – air heaters;12 – outlet of heat air on the burners;13 – air entrance after forced-draft fan;
14 – end combustion products outlet on the smoke exhaust.
The burning temperature may vary from100 ºС in the lower right sphere of the torch to 700 ºС in the upper central
sphere of the torch The system control may be carried out by means of two ways: due to the control of the fuel expense or the temperature control.
The present system controls the fuel expense, the temperature control is the subordinate parameter. The working out devise controls the temperature
that makes the process economically efficient. To date the control and management system of the gas fuel combustion process has the look,
represented at the picture 2. It was proved [1,2], that optimization of the burning process and, therefore the efficient use of gas is possible due to the
development of the additional control device elements, with the help of which the controlling of quantity of supplied fuel on the burner may help to manage
the torch structure, that is change the heat of convective surfaces.
Let’s analyze the structure of dry mass of the gas fuel:
CH4+C2H6+C3H8+C4H10+C5H12+N2
=100%,
if take the elements one by one, the percent quantity of substances makes: CH4=94,1%, C2H6=3,1%, C3H8=0,6%, C4H10=0,2%,
C5H12=0,8%, N2=1,2%
for the gas density at 0ordm;C and 760 Mmhg ρ=0,786кг/м3
Theme "Modification elements of the gas fuel combustion control system for its optimization of economic efficiency "
Analysis of the present researches
General outline. In the Ukrainian economy energy conservation and energy saving technologies are of primary implementation into the industry. Thereby, an important role plays detail and complex studies of heat and power resources and systems. Heat energy is an indispensable condition of human beings, society improvement, which one lives in, and provision of the humans’ everyday life. Industry systems optimization of heat energy production and discharge, adjustment of energy and water balances, energy saving and audit allow to improve heat and energy development perspectives, to raise technical and economic indexes of heat and energy equipment.
Efficiency, safety, security and economic efficiency of the heat and energy equipment of the boiler plants are determined mostly by the way of the fuel burns, perfection and efficiency of the choice of devices and equipment. The improvement of reliability and efficiency of heat supply depends on the work of the heat boilers, rationally projected heat scheme of the boiler room and wide implementation of the energy saving technologies, the fuel saving, heat and electric power.
To date, the gas problem in the world makes to reconsider the process of the fuel burning and improve the technologies for the coefficient of performance raise under the conditions of the reduction of the fuel resources expense. Modern science and industry technologies presuppose the use of the high temperature reactions to supply the heat system with the power source. The effectiveness of the power sources in the given terms (fro example the use of the gas mixture in the torch, in particular) should provide the maximum temperature and the efficiency of the fuel combustion.
Analysis of the present researches. Several papers are devoted to the problem connected with the heat and technical processes. For example, in the paper [3] the dependence of the water heating from the amount of the fuel supplied are taken into account. The researchers in terms of the optimal torch parameters for the water heating have been done. Rest on the achieved mathematical model of the heated up air heat exchange inside the combustion chamber with the convection surfaces of the heating[2], the theoretical data of the torch temperature in the different points of the environment are achieved. In this works is shown the following; the achievement of the maximum temperature for the particular burner is possible in terms of the oxidant and fuel optimal proportion supplied. The mixture of the components takes place in the working medium of the burner so that the prepared mixture of the initial components enter the torch (burner) nozzle. The received flame over the taking away from the nozzle is constant and axially symmetric. It allows us to use heat and power methods of the temperature determination. Nevertheless, these researches don’t touch upon the metrical matter and don’t make an accent on the choice of the transducers, which can be used in the aggressive high temperature medium with the less possible error.
Problem specification. Built up the mathematical model of the water heating form the fuel supplied to the system entrance, that will help to make the process more economically efficient due to the increase of the coefficient of performance of the boiler plant work. For this purpose it is necessary to make a study of the optimal parameters of the torch in the different points of the environment inside the burning chamber with the convectional surfaces of the heating. Take into account, that the torch is evenly spread inside the burning chamber, as the type of the burner is diffusive, that is the fuel is mixed up before the entrance to the burner.
Relevanceof the researches fulfilled in the present paper runs as follows; for the optimal arrangement of the combustion process and, therefore, effective use of gas, it is necessary to study the structures of the flame torch of the burner being used. [2]
Problem solution. Burning chamber represents an enclosed space with one in and out, into which the heat enters, and the smoke exhauster removes the end product of fuel combustion/
The structural scheme of burning chamber has a look shown at the figure 1:
1 – burning chamber; 2 –burner unit; 3 – drum;4 – vapour superheater;5 – steam cooler;6 – vapour superheater outlet chamber; 7 – remote cyclone collector; 8,9 – water economizers; 10,11 – air heaters;12 – outlet of heat air on the burners;13 – air entrance after forced-draft fan; 14 – end combustion products outlet on the smoke exhaust.
The burning temperature may vary from100 ºС in the lower right sphere of the torch to 700 ºС in the upper central sphere of the torch The system control may be carried out by means of two ways: due to the control of the fuel expense or the temperature control. The present system controls the fuel expense, the temperature control is the subordinate parameter. The working out devise controls the temperature that makes the process economically efficient. To date the control and management system of the gas fuel combustion process has the look, represented at the picture 2. It was proved [1,2], that optimization of the burning process and, therefore the efficient use of gas is possible due to the development of the additional control device elements, with the help of which the controlling of quantity of supplied fuel on the burner may help to manage the torch structure, that is change the heat of convective surfaces.
Let’s analyze the structure of dry mass of the gas fuel:
CH4+C2H6+C3H8+C4H10+C5H12+N2 =100%,
if take the elements one by one, the percent quantity of substances makes: CH4=94,1%, C2H6=3,1%, C3H8=0,6%, C4H10=0,2%, C5H12=0,8%, N2=1,2% for the gas density at 0ordm;C and 760 Mmhg ρ=0,786кг/м3
Figure 2 - Structural control and management system of the gas fuel combustion process
The lowest burning heat of dry gas fuel [4]:
QHP=358·CH4+637·C2H6+912·C3H8+1186·C4H10+1460·C5H12,
QHP=358·94,1+637·3,1+912·0,6+1186·0,2+1460·0,8=37614,9 kJ/h,
Fuel expense, m3/ s, supplied into the burning chamber, is determined according to the formula:
(1)
В= ∙100,
D=2,78 kg/s - boiler steaming capacity of steam generator DE-10-14GM;
пп=2928,4 kJ/kg – enthalpy of over-heated steam, determined according to [4], Table .P.10.
i’=855 kJ/kg – water enthalpy at a boiling temperature, according to [4] ,Table.P.9.
iпв=4,19·tпв=4,19·100=419 kJ/kg – feed water enthalpy;
tпв=100ºС–feed water temperature
The elaborated mathematical model should take into account the dependence of input parameters from output parameters. The existent measurement system is set on the fuel control and does not accounts for the spread of the temperature inside the burning chamber environment. It is suggested to take into consideration this fact and by that, provide the same heating of surfaces, but at a less fuel burning amount. The efficiency function of the elaborating device can be determined in the following way:
Еf=g(Ttorch,Нtorch)àmax. (2)
Нtorch - torch height; Ttorch- torch temperature at a particular point.
Knowing the amount of heat generated and the differential equation for the endless circular bar, the dependence of water heat from the fuel supply can be built up.
Тtorch=f(Rgas,Rair),
Нtorch=f(Rgas,Rair),
де Rgas,Rair-gas rate, air rate accordinglyIf we account for the fact the fuel consumption B (м3/c), is the function of gas and air flow (consumprion), therefore the mathematical model will run as following:
Тtorch, Нtorch=f(B),
Тw.outlet=φ(Нtorch,Тw.input), (3)
wherein Тw.input,Тw.outlet - water temperature at input and output accordingly
It is important to develop the torch control device at different flows of fuel, to make the specification table of the maximum torch temperature out if the fuel supply, at the absolute case, all the combusted fuel burns and the heat is spared for the surface heating. Proceeding from the achieved conditions it is necessary to control the fuel supply unless it helps to account for the loses at incomplete burning.
In this connection it is important to introduce the burning mechanism. The method, which allows it is as follows: temperature discharge in the torch and its measurement [4]. Usually the measured temperatures lie at a great distance from -273 ºС to 3000 ºС and more.
For the device realization it is necessary to define the number of control flame points in its different temperature sections. The temperature measurement can be done by means of contact and non-contact ways. The contact ways of measurement presuppose the contact itself with the object being measured. Nevertheless, the use of the contact thermometer leads to the flame structure distortion. As a result, consequently appearing measurement errors and delay of the indications depend on the physical characteristic and the flow speed of the measured environment near the thermometer and also on the thermometer construction. Such kind of errors may be greater than the methodical one. At the choice of the contact thermometer it should be taken under consideration, that the thermometer should stand the mechanical, chemical and thermal loads which it undergoes at the present object of the research.
In case of great temperatures and fast-flowing processes the optical measurement ways should be used, that possess the great space and time dimension.
The calculation of the actual temperature of the flame according to the measurement results can be done by one thermometer by the formula (4). We have received the developed ways of the temperature measurement, grounded on the dependence between the thermometer data and the diameter oermocothermocouple wire: in the particular flame point the thermometers are entered one by one (two or more) with the differen t thickness of the thermocouple wire and following the results of the measurement the actual torch temperature can be calculated.
wherein d - the diameter of the thermocouple wire; index "1" refers to the thin thermocouple wire, index w refers to the wall.
This and the majority of other methods don’t account for the radiating exchange between thermometer and flame. Disregard of this exchange of the dark flame does not lead to the great error of the measurement. In case of the luminous optically thick flame the radiating exchange between the thermocouple wire and the wall can be disregarded in comparison with the exchange between the thermocouple wire and the flame. Due to the powerful flame absorption, the thermometer cannot detect the wall. In this case the application of the formula (4) does not lead to the positive results. It is natural, that the wall or flame radiation influence also depends upon the measured point.
By practical application of the two thermometer method occur the same errors as the calculated before. That is why it is suggested to measure the temperature with the more thin thermoelectric thermometer. The order of the calculations is as follows:
Фk=α∙FTh∙(T-T1)≈σ∙ε∙FTh∙(T14-Tw4)=ФStr (5)
ε - radiating power;
FTh - thermometer surface.
After the transformation we will get the following formula:
T≈T1+KSo∙(T14-Tw4). (6)
Coefficient KSois calculated at a temperature Тw=300 К. The actual temperature is approximately given by the formula (6) into which the measured values Т1 и Тw and the values KSo, determined to the present temperature T1 and for the diameter of the wire d are introduced. Consequent on the mass the thermoelectric thermometers at a high-frequency turbulent vibration of the flame temperature cannot follow them exactly and give the average value of the temperature, attained by the integration of the first temperature degree in time. At the contact thermal converter measurements the valid errors can occur, conditioned by heat elimination from the sensor element by means of thermal efficiency along the cover and heat extraction by the radiation.
The error Δt of the gas temperature measurement, caused by the radiant heat exchange between the thermal converter cover and the tube wall can be determined from the вираження:
wherein ТС, ТТ, ТСТ – the environment, thermal converter and wall temperatures accordingly, K; temperature
αК - coefficient of the thermal efficiency by the convection between thermal convector and the measured environment, Wt/(m2∙К); С0=5,67Wt/(m2∙К) - the radiance coefficient of the absolute blackbody radiator; εПР- the reduced factor of the heat radiance, which characterizes the heat exchange between the thermal converter and the wall.
When the wall surface is much bigger that the thermal convector surface (FСТ>>FТ), it may be counted that the reduced factor of the heat radiance is almost equal to the heat radiance coefficient of the thermal convector (εПР=εТ).
The temperature measurement error Δtby means of the heatsink along the cover is calculated according to the formula:
wherein α - coefficient of the thermal efficiency between thermal convector and the measured environment Wt/(m2∙К); Р и S – perimeter, m, and square m2 cross-section area of the thermal converter cover
λ- coefficient of thermal conductivity of the thermal converter, Wt/(m∙К);
l -depth of the cover embedding into the measured environment, m.
The analysis, which is mentioned above shows that for the choice of the control points it is necessary to study the torch structure for the further flame control in it. Geometrical torch represents tapering axially symmetrical structure (Pic.3). Sections were chosen by the following way: 1 section – near the nozzle of the burner, 2 section – at a distance 1/3 of the whole length of small cone, 3 section – at a distance 2/3 of the whole length of small cone, 4 section – on the top of the small cone. Inside the large cone of the light blue colour the small cone of the deep blue colour can be traced. The yellow illumination zone is situated at the top of the small cone (inside cone) to breakdown of heavy carbon and formation of condensed dispersion phase of carbon (carbon char) described in the work [5], accordingly.
Therefore, the achieved structure of the torch is determined by the regime of the diffusive fuel burning (propane/butane mix used in appliances and air oxidant) with the grade-wise kinetic component (and temperature) increase, which runs to it maximum meaning at the bottom fringe of the yellow illumination zone. In course of this experiment the parallel research in heat-technique trend was noticed [2], in which the experimental data was attained for the furnace device, given in Table 1. .
From the experiment results, attained in the work [2] it is seen, that the temperature measurements are necessary to make in different points of section to determine the distribution of flame in the furnace chamber environment. Measurement in the torch middle is proved theoretically by the experimental data, the temperature along the height should be maximum in each section. Data in the remote points of visible torch area are located more closely to the convectional surfaces, that’s why it is very important. The air feed is regulated by means of the burner gap diffusor widening, that provides air intake into the working volume of the burner. The possibility to regulate it is limited and is done chiefly with the change of fuel (gas) feed supply into the working volume.
Table 1 – experimental data in different torch sections
| section 1 |
r, мм |
Т, ºС |
section 2 |
r, мм |
Т, ºС |
|
5 |
0 |
170 |
5 |
0 |
560 |
|
4 |
2.75 |
440 |
3 |
4,63 |
640 |
|
3 |
6.13 |
530 |
2 |
5,69 |
600 |
|
2 |
6,81 |
485 |
1 |
6,81 |
420 |
|
1 |
7,5 |
420 |
|||
| section 3 | section 4 | ||||
|
5 |
0 |
650 |
5 |
0 | 700 |
|
3 |
2,38 |
640 |
2 |
2,31 | 600 |
|
2 |
4,02 |
630 |
1 |
4,36 | 420 |
|
1 |
5,59 |
420 |
As the thermoelectric sensor the chromel-alumel differential thermocouple can be used. The hot end
of thermocouple, embedded into the flame, is attached on the electrolyzing theflon support, mounted
on the substage, the construction of which allows the vertical and horizontal movements, that provides
possibility to measure the temperature in any torch point [2].
Figure 4 - System work
Conclusions:
1. The general mathematical model of the water heat is built up. It is noticed that the water heat differs form the fuel feeding system by the control, which is done according to the temperature inside the furnace not the consumption. This allows to increase the efficiency due to the decrease of fuel expense.
2. It is stated that the hypothetical data are the same as theoretical ones, that is, they have the same tendency of the temperature discharge in torch and give arguments to the possibility of the present control and management system modification.
3. The researches in different points inside the furnace chamber for the optimal torch parameters have been done. It is stated that the function of modification elements will have the installation of thermal converters in the central and fringe points of the flame. It is worth to mention that it is necessary to change contact temperature sensors for non-contact, which will provide the research possibility of the high dynamic temperature spread of flame in the environment.
Literature
1. Киселев Н. А. – Котельные установки. Учеб. пособие для техн. училищ. М., «Высш. школа», 1975, 277 с.
2. Трофименко М.Ю. Особенности структуры факела пламени твердых смесевых систем на основе перхлората аммония. Диссертация на соискание степени канд. физ.-мат. наук, Одесса, 1999.
3. Тепловой расчет котельных агрегатов (нормативный метод). Кузнецов Н.В., Митор В.В., Дубовский И.В., Карасина Э.С. -М.: Энергия, 1973
4. Тепловой расчет котельных агрегатов [ Учебное пособие] А. С. Попов, И. Л. Дунин; Рост. инж.-строит. ин-т 119 с., [2] л. табл. ил. 20 с.
5. Гейдон А.Г., Вольфгард Х.Г. Пламя, его структура, излучение и температура. Пер. с англ. –М: Металлург, 1959. -333 с.
6. Евдокимов Н. И. Методы и средства исследований. Ч. 1 Температура. Российский гос. университет нефти и газа им. И. М. Губкина.
7. Двойнишников В. А.,,Деев Л. В. Конструкция и расчет котельных установок: Уч. для техникумов по специальности "Котлостроение". М.: Машиностроение, 1988. - 264 с. ил.
8. В. С. Мухин, И. А. Саков Приборы контроля и средства автоматики тепловых процессов. М: Высшая школа 1988 - 256 с.
9. Качан А. Д. - Режимы работы и эксплуатации ТЭЦ, Минск: Вышэйшая школа
10. М. М. Щеголев Топливо, топки и котельные установки М.: Литературы по строительству и архитектуре. 1953
The torch is stable approximately till the yellow illumination zone, situated at a distance of ¾ of the torch length, beginning with the nozzle middle. This instability has determined impossibility of getting the precise measurements of temperatures in the top quarter of the torch.
Along the torch axis the temperature rises according to the moving away from the nozzle middle and reaches maximum at the bottom fringe of the yellow illumination zone. Further measurement detects the fall of the flame temperature.
Therefore, the burning mechanism near the nozzle middle carries diffusive character. As far as moving along the torch, the mixing of the oxidant and fuel becomes better and the definite role starts playing the kinetic component, which determines the rise of temperature near the yellow illumination zone. As far as the temperature stability of the big cone fringe is concerned, it is determined by the diffusion of oxidant from the outer air into the reaction zone [5].
