GB2042221A

GB2042221A - Automatic control of burner combustion

Info

Publication number: GB2042221A
Application number: GB7912551A
Authority: GB
Original assignee: Kobe Steel Ltd
Current assignee: Kobe Steel Ltd
Priority date: 1979-02-16
Filing date: 1979-04-10
Publication date: 1980-09-17
Also published as: FR2449249A1; JPS6112170B2; DE2914792C2; GB2042221B; DE2914792A1; FR2449249B1; CA1149905A; JPS55110823A

Abstract

The invention discloses a method of determining the state of combustion and an apparatus for said method in which, in carrying out the combustion in various industrial furnaces, a minute combustion pressure pulsation is detected in order to determine the combustion state. The invention discloses also a method of using the results of this determination for combustion control and an apparatus for said method, enabling reduction of environmental pollution and improvement of the combustion efficiency. The pressure pulsation may be determined acoustically.

Description

SPECIFICATION Combustion state determination method and apparatus This invention relates to a combustion state determination method and more particularly to a method of quantitatively determining the combustion state inside a furnace on the basis of the minute pressure pulsation pattern superimposed on the pressure inside the furnace, to an apparatus for carrying out said method and also to a method and an apparatus for controlling the combustion inside the furnace on the basis of the results of the determination.

In burning various kinds of fuels in a variety of industrial furnaces using a burner or the like, it is a matter of the utmost importance to properly determine the combustion state to prevent environmental pollution by nitrogen oxides (NOx) or smoke involved in the combustion, for the improvement of the combustion efficiency or for heat management such as the effective use of heat.

It has hitherto been possible in a combustion test furnace to qualitatively evaluate the combustion state to a certain extent by inspecting the temperature distribution or the gas distribution of the flame through sampling holes formed on the furnace body. However, since a great deal of time and labour are required for their measurement, the determination is generally made by observing the flame with the naked eye.

On the other hand, commercial furnaces are not equipped with sampling holes for reasons of structural strength or to save energy loss and few are equipped even with an observation hole. Hence, judgement of the combustion state has hitherto been extremely difficult.

In any case, only unreliable evaluations of the combustion state have so far been possible using visual observation of whether the flammability is good or bad or the combustion is rapid or slow.

In order to make effective the management of heat or pollution prevention inside a combustion furnace, it is necessary to control the combustion state. For this purpose an effective method of rapidly and quantitatively determining the combustion state inside the furnace is necessary. If such determination method is possible, full automatic control of the combustion can also be realised.

Accordingly, the inventors of the present invention have made intensive observation and examination in detail of the combustion state under various combustion conditions using a combustion test furnace and surprisingly have found that there is a minute pressure pulsation below about 20 mm water pressure superimposed on the pressure inside the furnace which changes in a predetermined way in accordance with the change in the combustion state.As a result of further studies, the inventors have also found that the combustion states such as the combustion speed inside the furnace, the flame length, the property of the flame (transparent flame, luminous flame, etc) the smoke amount and so forth are refiected clearly in the minute pressure pulsation pattern inside the furnace and that the power spectral density distribution obtained by converting the minute pressure pulsation pattern signal can be used effectively in a practical application as an index for the determination of the combustion state.

The present invention provides a method of determining the combustion state in which the minute combustion pressure pulsation is detected and the combustion state is determined on the basis of this minute pressure pulsation pattern.

The present invention also provides a method of controlling a combustion state limiting factor in the combustion inside a furnace in which the pressure pulsation inside the furnace is detected and compared with a pulsation waveform corresponding to a desired combustion state and the combustion state limiting factor is controlled on the basis of that comparison.

The present invention further provides an apparatus for determining a combustion state in a furnace including: means for detecting a minute combustion pressure pulsation inside a furnace caused by the combustion and converting it into an electric signal; means for amplifying said electric signal; and means for analysing the amplified electric signal into its frequency components.

The invention also provides an apparatus for determining a combustion state in a furnace including: means for detecting a minute combustion pressure pulsation inside a furnace caused by the combustion and converting it into an electric signal; means for amplifying said electric signal; means for analysing the amplified electric signal into its frequency components and comparing them with a predetermined value; and means for adjusting and controlling combustion state limiting factors on the basis of a deviation signal obtained as a result of the comparison.

The method and apparatus of the invention will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1 fix is a vertical axial section and Figure 1/11] is an end view of a combustion test furnace, Figure2 is a part section of various burner tips, Figure 3 is an enlarged schematic view of part of Figure 1A showing various positions of the principal portion of the burner installation, Figure 4 is a block diagram of apparatus for measuring the pressure pulsations, Figures 5to 21 are sets of charts each showing a minute pressure pulsation pattern wherein (A) shows the waveform and (B) shows the corresponding power spectrum, Figure 22 is a schematic diagram of measuring apparatus for measuring the minute pressure pulsations in accordance with the present invention, Figure 23 is a schematic diagram of combustion state determination apparatus in'accordance with the present invention, Figure 24 is a schematic diagram of combustion control apparatus in accordance with the present invention, Figure 25 is a schematic diagram of combustion air quantity (excess air ratio) controlling apparatus in accordance with the present invention, Figure 26 is a schematic diagram of an atomising quantity controlling apparatus in accordance with the present invention, Figure 27 is a schematic diagram of a burner position controlling apparatus in accordahce with the present invention, Figure 28 is a schematic diagram of combustion air controlling apparatus in accordance with the present invention, Figure 29 is a schematic diagram of an atomising quantity controlling apparatus in accordance with the present invention, and, Figure 30 is a schematic diagram of a burner position controlling apparatus in accordance with the present invention.

Use of the principles of the present invention enables one to accurately make quantitative determination of the combustion state inside various furnaces such as industrial combustion furnaces using various types of gas or liquid fuels by detecting the minute pressure pulsations in the pressure inside the furnace by means of a pressure detection probe disposed in front of a burner inside the furnace. The minute pressure pulsation signals so obtained are converted into a pulsation pattern represented for example by a power spectral density distribution which may be used as an index to determine the combustion state.

Combustion is a phenomenon comprising the oxidation reaction of molecules of inflammable matter and involves light and heat, thereby producing flame. Inside the furnace, there occurs random minute pressure pulsations (generally up to about 20 mm water pressure) superimposed on the basic pressure inside the furnace even during normal combustion due to the "flicker phenomena" or the "intermittent phenomena" of the flame or to the local density fluctuations arising from the combustion of the turbulent diffusion flow.

We have found that the combustion state can be expressed in terms of this minute pressure pulsation inside the furnace and have established a technique enabling one to measure the combustion state rapidly and quantitatively by measuring the pressure inside the furnace without measuring the flame temperature distribution and the gas distribution as is required by conventional techniques.

The combustion state inside the furnace varies depending on the combustion conditions determined by such factors as the shape of burner tips, the positions of the burner tips, the excess air ratio and so forth. We have found, however, that, irrespective of these factors, a certain combustion state corresponds to a particular minute pressure pulsation pattern inside the furnace. Thus a specific minute pressure pulsation pattern for a particular combustion condition always represents a specific combustion state.

A detailed explanation will now be given on the relationship between the combustion state and the minute pressure pulsation pattern when the factors such as the shape of the burner tips, the excess air ratio or the like are varied. The following combustion test is carried out using the combustion test furnace (inner diameter 1 m x length 4m) shown in Figures 1 [I] and [II]. The fuel and the air are respectively fed for combustion from a burner (3) and a fuel assitantfeed port (4) inside a burner tile (refractory block) (2) of the main body (1) ofthefurnace and at the same time, the minute pressure pulsation is.detected by a pressure pulsation detector (5) in front of the burner (3) while the flame is inspected from an inspection hole (6) at the tail of the furnace.The exhaust gas is sampled from an exhaust sampling hole (7) of the flue; The configuration of the burner tips, the tip position ofthe burner and the excess air ratio are varied. Three configurations of the burner tips are shown in Figures 2 [li, [Il], [III]. Figure 2 [1] shows the so-called ordinary type which has several jet holes (a) arranged so that their axes are directed away from the axis of the burner and provides the highest miscibility between the fuel and the air for combustion, thus providing good combustibility. Figure 2 [Il] shows the so-called straight type which has one jet hole (b) on and parallel to the burner axis which provides a miscibility of fuel and air between the above mentioned ordinary type and the eccentric type to be next described.Figures 2 [111] shows the so-called eccentric type which has a jet hole (c) whose axis is at a predetermined angle of inclination with respect to the burner axis and which provides mild miscibility, thereby allowing the combustion to proceed gradually.

As shown in Figure 3, the tip of the burner may be selectively placed at positions (a) - (g) from the furnace inner surface (F) of the burner tile (2) towards an air resister (8) at the back of the burner tile. Numerical values in the drawing represent the distance from the furnace inner surface (F) of the burner tile (in mm). The normal position would be near the point c (370 mm) for the gas type fuel and near the point d (470 mm) for the liquid fuel.

The excess air ratio may be changed in four stages over the range from 0.5 - 9.5% in terms of the 2 concentration of the exhaust gas.

As to the other combustion conditions, the combustion quantity is 40 x 104 Kcal/Hr, the temperature of the air for combustion is 3200C and the open angle of the burner tile is 30 degrees and each of these values is kept constant whilst the above mentioned factors is varied one by one.

As a measuring instrument for the minute pressure pulsations inside the furnace, there is used an apparatus capable of amplifying the pressure detected by a pressure detector using a wire strain gauge, arranged so that one may directly read out the pressure on a meter and also record the output voltage from record output terminals. Figure 4 shows a block diagram of this apparatus wherein reference number (8) represents a pressure pick up probe; (9) is a detector; (10) is an amplifier; (11) is a stylus oscillograph and (12) is a data recorder. The pressure pick-up probe is fitted at right angles with respect to the axial direction of the flame at a position by 400mm ahead of the furnace inner surface (F) of the burner tile (see Figure 3) and its tip protrudes by 200 mm from the side wall of the furnace.The detector (9) is a pressure transducer using a wire strain gauge and its strain quantity is 430 x 10-6 at 20 mm water pressure. The amplifier (10) is a dynamic strain gauge and its output is 2V per 20 mm water pressure. The oscillograph (11) records the waveform for observation and the data recorder (12) stores the waveform analysis data on a magnetic recording tape.

Figures 5 to 16 show the minute pressure pulsation patterns inside the furnace when the shapes of the burner tips, the tip positions of the burner, the air ratio and so forth are varied. In each Figure, the graphs (A) represent the waveforms recorded by the stylus oscillograph and the graphs (B) represent the density distribution of the pulsation energy obtained by subjecting the pulsation signal stored in the data recorder to a power spectral density analysis. The waveforms shown in graphs (A) are a part of the record obtained by recording only the pulsing part of the pressure in the furnace by removing the background pressure inside the furnace so that the ordinate represents the pulsation pressure (mmH2O) and the abscissa represents the time (second).The power spectra shown in graphs (B) represent the pulsation energy per unit number of pulsation of the irregular pulsation shown in graph (A) wherein the ordinate represents the energy density and the abscissa represents the frequency (Hz) within the range of from 0 to 45 Hz.

In the above mentioned analysis, the data of the measuring time of about 2 minutes are used and 100 Hz is divided approximately equally into 1000 and then digitalised.

Incidentally, the power spectral density of the random fluctuation can be obtained by the following equation;

wherein 2T is an analysis time (zone); y is pulsation pressure; and t is time.

The power spectral density can be obtained by the Fourier transformation of the above mentioned equation; Power spectral density P(f)

wherein X is a time interval for reading the waveform; f is a frequency and i is a complex number.

Figure 5 [I] - [VII] shows the minute pressure pulsation patterns when the combustion is made using butane gas as the fuel and the ordinary type of burner tip shown in Figure 2 [I], and adjusting the excess air ratio so that the exhaust gas 02 concentration becomes 3.0 + 0.2% with the other combustion conditions being at the respective predetermined values as mentioned previously and when the tip position of the burner is varied. The tip position of the burner is at the point (a) (70 mm, see Figure 3) for [I], at the point (b) (270mm for [II], at the point (c), (370 mm) for [III], at the point (d) (470 mm) for [IV], at the point (e) (570 mm) for [V], at the point (f) (670 mm) for [VI] and at the point (g) (770 mm) for [VII].

As to the combustion state initially, the closer the tip position of the burner is to the inside of the furnace, the slower the combustion whereby the shape of the flame is great and exhibits the long flame. As the burner position is moved away from the inside of the furnace, the flame becomes shorter until the flame becomes a transparent flame and the combustion changes into the rapid combustion state approximate to the so-called premix combustion flame.

When the pulsation waveforms shown in Figure 5(A) are examined along with the change of the combustion state, it is found that the pulsation describes a large and gradual waveform (Figure 5 [I], [II] ) when the combustion is slow (when the burner position is near the inside of the furnace), the waveform changes from a large waveform to small one as the combustion changes to the rapid combustion state, and the frequency increases and becomes extremely high when there is a transparent flame (Figure 5 [VI], [Vll] When the change in the above mentioned waveforms is examined with reference to the results of the power spectral density analysis shown in Figure 5(B), it is found that whereas the frequency components of about 2 - 4Hz are the principal components of the minute pressure pulsation in the slow combustion state (Figure 5 [I], [II], etc.) the principal components shift to about 12 - 13Hz as the combustion becomes quicker (Figure 5 [III]) and further to about 20-25Hz (Figure 5 [VI], [Vll]).

As the combustion shifts from the slow state to the rapid state near the premix flame in this manner, the frequency components of the minute pressure pulsation inside the furnace tend to increase and hence, it is seen that the combustion state corresponds to the pulsation pattern.

Figure 6 shows the pulsation pattern for combustion under the same conditions as the above mentioned Figure 5 except that the straight type (Figure 2 [Il]) of burner tip is used, and the tip position of the burner is varied. Figures 6 [I] - [VII] correspond respectively to the cases where the tip positions of the burner are atthe points (a) - (g) (see Figure 3).

Since the straight type burner tip in this embodiment has inferior miscibility in comparison with the ordinary type burner tip, the luminous flame is present even at the point (d) in the case of the straight type whereas in the case of the ordinary type the combustion becomes rapid and the flame is almost transparent at the point (d). Though there is such a difference in the combustion state, it is confirmed that the same predetermined relationship exists between the combustion state and the pulsation pattern as in the case of the ordinary type burner tip shown in Figure 5.In other words, when the combustion is slow and the size of the flame is great, the pulsation waveform is large and gradual and its power spectrum consists principally of the frequency components of about 2 - 5 Hz (Figure 6 [1] - [Ill]). As the combustion becomes rapid, the power spectrum exceeds about 1OHz and shifts to 20 - 25 Hz (Figure 6 [V] - [Vlll ).

When the difference in the combustion state is observed from the pulsation pattern by placing respectively the ordinary type burner tip and the straight type burner tip at the same position, eg at the point (d), the power spectrum in the former no longer contains the frequency components of 2 - 4Hz but consists principally of 20 - 25Hz (Figure 5 [IV]), whereas the frequency components of 2 - 4 Hz still remain in the latter (Figure 6 [IV] ). It is thus assumed that the combustion state is slower in the straight type than in the ordinary type.

Figure 7 shows the pulsation pattern when the position of the burner tip is varied under the same conditions as in Figure 5 except that the eccentric type of burner tip (Figure 2 [III]) is used. Figures 7 [I] - [IV] correspond respectively to the burner tip positions at the points (a), (b), (c) and (d). The combustion state is relatively slow over the range (a) - (d) and a considerable quantity of the luminous flame is still observed even at the burner position (d). As to the pulsation pattern, on the other hand, the waveform is loose in each case and the frequency components are primarily about 2 - 4Hz, thus indicating that the combustion state is slow (Figure 7 [i] - [IV]) and that the miscibility is lower than in the case of the ordinary type or straight type burner tip.

In each of the aforementioned combustion experiments, the burner tip position is the variable factor. The relationship between the combustion state and the minute pressure pulsation pattern is next measured under the same condition as in the aforementioned experiments except that the burner tip position is fixed at the point (c) and the air ratio is the variable factor (whereby the adjustment of the air ratio is expressed in terms of the percentage of the exhaust gas 2 as an index). The results are shown in Figures 8 - 10.

Figure 8 shows the results when the ordinary type of burner tip (Figure 2 [I] ) is used wherein [I] shows the pulsation pattern when the exhaust gas 2 iS 0.75%, [Il] shows the pulsation pattern when the exhaust gas 2 is 3.1%, [lil] shows the pulsation pattern when the exhaust gas 2 iS 6.4% and [IV] shows the pulsation pattern when the exhaust gas 2 iS 9.3%.

In this case, the combustion is slow and the luminous flame can be observed on the far low 2 concentration, but the flame becomes transparent and the combustion shifts to the rapid combustion state for higher O2 concentration. Underthe condition where the exhaust gas 2 iS at the lowest value of 0.75%, the combustion also is the slowest and its frequency components are principally of about 2 - 4Hz (Figure 8 [I]).As the 2 concentration is gradually increased, however, the principal frequency components shift to about 10 - 15 Hz ([II], [III]). When the 2 concentration is further increased to attain the rapid combustion state, the frequency components as high as about 20 - 27 Hz are dominant ([IV]).

Figure 9 shows the case where the straight type tip (Figure 2 [Il]) is used wherein [I] shows the case where the exhaust gas 2 iS 0.6%, [lii shows the case where 2 iS 3.1%, [III] shows the case where 2 is 6.2% and [lV] shows the case where 2 iS 9.35%. In the same way as in the cases shown in Figure 8, the increase in oxygen improves the combustibility.Since the miscibility is lower in this case than in the case of the ordinary type, tip, the combustion state is slower even at the excessive 2 of about 6% and the frequency components corresponding thereto are principally of about 2 - 4Hz up to the 2 concentration of about 6%. When 2 iS about 9%, the combstion shifts to the rapid combustion and its frequency also shifts to about 20 - 25 Hz.

Figure 10 shows the case where the eccentric type tip (Figure 2 [Ill]) is used wherein [I] shows the case where the exhaust gas 2 iS 1.0%, [ll] shows the case where 2 iS 3.0%, [III] shows the case where 2 is 6.4% and [IV] shows the case where 2 iS 9.3%. In comparison with the ordinary type tip and with the straight type tip, the combustion state is slower at the same percentage of 2 and its frequency components are principally of about 2 - 4Hz. Even at the time of combustion of a higher percentage of 2, the frequency components of high frequency are extremely small and this corresponds to the fact that the combustion state is slow.

As described in the foregoing paragraph, it is obvious that the combustion state and the minute pressure pulsation pattern inside the furnace exhibit a specific correlation when the combustion is carried out by using butane gas as the fuel and burner tips of the ordinary type, the straight type and the eccentric type and by varying the burner tip position or the air ratio (excessive air amount). Where the combustion is slow and the luminous flame is present the power spectrum consists principally of low frequency components of about 2 - 4Hz, and where the combustion is rapid and the transparent flame is present, the frequency components shift to higher components of about 20 - 25 Hz. Thus, this predetermined tendency has been confirmed. Clear correspondence is also observed in the difference in the miscibility arising from the shape of the burner tip. Namely, it is found that the combustibility becomes rapid even at the exhaust 2 of 3% with the ordinary type tip and the frequency components of about 20 - 25 Hz are dominant whereas the combustion state is slow even at the exhaust 2 of 9.8% and the frequency is still in the low range of about 2 4Hz in the straight type and the eccentric type tip.

Next, the correlation between the burner tip position and the combustibility and its minute pressure pulsation pattern is examined when burning kerosene instead of the butane gas used in the aforementioned experiments and also using each of the ordinary, straight and eccentric types of burner tips. The air ratio is set to give an exhaust gas 2 of 3.0 + 0.2%. The burner is a commercially available steam system intermixing type gas burner and high pressure air is used as an atomising fluid. The results are shown in Figures 11 - 13, respectively.

Figure 11 shows the results of the experiments using the ordinary type burner tip wherein Figures [I] to [II1] represent the cases where the burner tip positions are at the point (a) (70 mm), at the point (b) (270 mm) and at the point (d) (470 mm), respectively.

It is found that there is the same general relationship between the influence of the burner position and the pulsation pattern on the combustion state for kerosene as for butane. Namely, when the burner tip is near the inside of the furnace, the combustion is slow, but when it is located at the point (d), the combustion gradually provides a transparent flame and shifts to a rapid combustion state. The waveform correspondingly changes from a large and loose waveform to a waveform of a high frequency. The frequency components are principally about 2 - 4Hz during the slow combustion (Figure 11 [1], [II1) but as the combustion shifts gradually to the rapid combustion, the components of about 2 - 4Hz decrease and those of about 10 - 15 Hz and of about 20 - 25 Hz start appearing (Figure 11 [III]).The correlation between the combustion state and the pulsation pattern is exactly the same as in the aforementioned experiments using butane gas as the fuel.

Figure 12 shows the results of the experiments using the straight type tip wherein [ll - [Ill] show the cases where the burner tip is located at the point (a), at the point (b) and at the point (d), respectively.

At each of the points (a) - (d), the degree of the luminous flame is stronger in comparison with the case when the ordinary type burner is used and the frequency possesses components of a higher range of about 30Hz, (Figure 12 [IIIl).

Figure 13 shows the results of the experiments using the eccentric type burner tip wherein [I] - [Ill] show the cases where the burner tip is located at the point (a), at the point (b) and at the point (d), respectively. In each case, the combustion state is slow and the frequency components are in the low range of about 2-4Hz.

Figures 14 and 15 show the combustion state and the pulsation pattern when using kerosene as the fuel in the same way as the above mentioned experiments, fixing the tip of the ordinary or eccentric type burner respectively at the point (d) (470 mm), and varying the air ratio.

Figure 14 shows the results of the experiments using the ordinary type tip wherein [I], [II] and [III] represent the cases where the exhaust gas concentration of 2 iS 2.95%, 6.55% and 9.4% respectively. Though the luminous flame is observed for low 2 values the transparent flame is observed for high 2 values. The frequency distributes over the wide range of about 2 - 4 Hz, about 10 - 15 Hz and about 20 - 30Hz for low 2 values ( [ll), but consists principally of high frequency components ofabout 20-16Hz for high 2 values ([II], [III1). Thus, the frequency tends to shift to higher frequency components with an increasing speed of combustibility.

Figure 15 shows the results of experiments using the eccentric type tip wherein [I], [Il] and still show respectively the cases where the exhaust gas 2 iS 0.3 -0.6%, 3.05%, 6.5% and 9.6% respectively. The combustion is slow when the exhaust gas Oz is up to 6.5%, but it approaches a transparent flame when the exhaust gas 2 iS 9.6%.On the other hand, the frequency components are principally of about 2 - 4Hz for low 2 values ([i] - [Ill]) but exhibits a pulsation pattern having a greater proportion of components of about 10 15 Hz and about 20 - 25 Hz when the exhaust Oz iS 9.6% ([IVl).

As explained above, the combustion state and the pulsation pattern again exhibit a predetermined correlation irrespective of the kind of the combustion factors varies even when kerosene is used as the fuel.

Where the combustion is slow and a large soft flame is formed, the frequency components are principally of about 2 - 4Hz. As the combustion becomes quicker, the frequency components contain those of about 10 - 15 Hz and further those of about 20 - 26Hz. It is thus obvious that detection of the pulsation pattern enables one to estimate the combustion state.

Figures 16 - 19 show the pulsation pattern and the combustion state when the combustion is carried out using a heavy oil as the fuel and when either the burner tip position or the air ratio is varied as the variable factors for the combustion condition. Incidentally, when the burner position is used as the variable factor, the air ratio is fixed to provide an exhaust gas 2 of 3.0% + 0.2%, while the burner tip position is fixed at the point (d) (470 mm) when the air ratio is used as the variable factor. The burner and the atomising fluid are the same as those used in the aforementioned experiments using the kerosene fuel.

Figure 16 shows the results of experiments wherein the ordinary type of burner tip is used and the burner tip position is changed. Figures 16[1], [Il] and [Ill] represent the pulsation patterns when the burner tip is located at the point (a), at the point (b) and at the point (d), respectively.

Figure 17 shows the results of experiments wherein the eccentric type of burner tip is used and the burner tip position is changed. Figures 17 [1], [Il] and [III] represent the pulsation patterns when the burner tip is located at the point (a), at the point (b) and at the point (d), respectively.

Figure 18 shows the results of experiments wherein the ordinary type of burner tip is used and the exhaust gas 2 (%) is changed. Figures 18 [I], [il], [III] and [IV] represent the pulsation patterns when the level of exhaust gas 2 is 0.6%, 3.1%, 6.6% and 9.5% respectively.

Figure 19 shows the results of experiments wherein the eccentric type of burner tip is used and the exhaust gas 2 (%) iS changed. Figures 19 [I], [II], [III] and [IV] represent the pulsation patterns when the exhaust gas 2 iS 3.1%, 6.3% and 9.15%, respectively.

The following may be summarised from the pulsation pattern and the combustion state shown in Figures 16 - 19. The pulsation pattern consisting principally of the frequency components of about 2 - 4Hz is detected when the combustion state is judged as being slow from a flame photograph in the same way as in the aforementioned experiments and on the other hand, when the flame turns to be a sharp short flame and the combustion is judged as being rapid, the frequency components of about 10 - 15Hz and about 20 - 27Hz are detected.

The correlation between the combustibility due to the burner tip and the pulsation pattern, is confirmed by carrying out the combustion using a straight type burner tip, which is made especially and has a varying fuel injection speed using butane gas as the fuel while changing either the burner tip position or the air ratio as the variable combustion factor. The other combustion conditions are the same as those in the aforementioned experiments, ie a combustion quantity of 40 x 104 Kcal/hr, an air temperature of 320"C and an open angle of the burner tile of 30 degrees. When the burner position is varied, the air ratio is fixed to give the exhaust gas 2 content of 3.0% + 0.2% while the burner tip position is fixed at the point (c) when the air ratio is used as the variable factor.The results are shown in Figures 20 and 21.

Figure 20 shows the results of experiments wherein the burner tip position is varied. Figures 20 [I] to [IV] represent the cases where the burner tip is located at the point (a), at the point (b), at the point (c), at the point (d), at the point (e) and at the point (f), respectively. According to this, the combustion is slow when the burner tip position is up to the point (b) (270 mm), starts shifting to rapid combustion already at the point (c) (370 mm) and becomes a transparent flame at the point (d) onwards.In response to the change of the combustion state, the frequency of about 10 - 25 Hz starts appearing in the pulsation pattern already at the point (c) and the low frequency of about 2 - 4Hz disappears at this point ([III]). Thereafter, the pulsation pattern has a principal frequency of about 20 - 25Hz as can be seen at the subsequent points (d) - (f). It is confirmed therefore that this burner tip has a flammability as good as the aforementioned ordinary type tip.

Figure 21 shows the pulsation pattern when the air ratio is changed wherein [I] through [IV] represent the cases where the exhaust gas 2 level is 0.8%, 3.0%, 6.3% and 9.45%, respectively. As can be seen from these charts, the combustion is good even when the exhaust gas 2 iS below 1% and its frequency contains the components of about 10 - 25Hz ([I]). As the exhaust gas 2 exceeds this level, the combustion becomes more rapid and provides a transparent flame at an 2 level of 9.45% and the corresponding pulsation pattern frequency consists principally of about 20 - Hz. Hence, the combustibility of the tip is found to be as good as the ordinary type burner tip.

As can be appreciated frqm the foregoing explanation, when the variable combustion factors are changed, the combustion state is reflected by the minute pressure pulsation pattern superimposed on the pressure inside the furnace, irrespective of the kinds of gas or liquid type fuels used and irrespective of the shape of the burner tip. Accordingly, it is obvious that the combustion state inside the furnace can be propertly judged from the pulsation pattern. Namely, when the combustion proceeds slowly and a large long flame is formed, there is detected a pulsation pattern having frequency components of about 2 - 4Hz and as the combustion changes to a rapid state, it provides a pulsation pattern having about 20 - 25Hz. The pulsation pattern and the combustion characteristics in the combustion test furnace may be summarised as shown in Table 1.

TABLE 1 Relation between the pulsation pattern and combustion characteristics Frequency Combustion characteristics characteristics 1 Only components of Combustion state is Fig. 6 [I] about 2 - 4hz extremely slow.

Large and soft flame Fig. 9 [Il] is formed.

Some is apt to occur. Fig. 11 [I], etc.

2 Consists principally Combustion is still slow. Fig. 5 [III] of about 2 - 4Hz and Though flame is large, Fig. 8 [I] contains components less column of flame of about 10 - 15Hz Fig. 15 [IV] and about 20 - 25 Hz. Fig. 18 [I],etc.

3 Components of about Ordinary combustion Fig. 5 [IV] 2 - 4Hz become less state.

and those of about Flame becomes sharp. Fig. 6 [IV] 10 - 15Hz and about 20 - 25Hz are Fig. 14 [III] dominant.

4 Components of about Combustion becomes Fig. 5 [VI] 2 - 4Hz disappear. quicker and sharp Components of about shortflame is Fig. 20 [IV] 10 - 15Hz become formed.

smaller and those Combustion begins to Fig. 21 [III], of about 20 - 25Hz provide trans- etc.

are dominant. parent flame in case of gas fuel.

5 Only components of Rapid combustion state. Fig. 6 [Vll] about 20 - 25Hz Transparent flame in the case of the gas Fig. 14 [IV] fuel. Very few luminous flames even Fig. 20 [VI], in the liquid fuel. etc The frequency range corresponding to the above mentioned specific combustion state is not necessarily stationary, but exhibits particular frequency components in accordance with the type and the capacity of various kinds of furnaces. It contains a range of low frequency components such as about 2 - 4Hz when the size of the flame is large and the combustion is slow and changes to include a range of higher frequency components as the combustion becomes quicker. Furthermore, in the combustion state where the flame tends to become transparent or near thereto, only the high frequency components of about 20 -25 Hz appear.

Thus there is a predetermined frequency peculiar to a given furnace whilst in a specific combustion state. If the pulsation patterns particular to the various combustion states of a given combustion furnace are known in advance, therefore, it becomes possible to accurately judge the combustion state of that furnace merely by detecting the pulsation pattern.

Furthermore, if determination is made in advance how much the combustion characteristics change and how much and how the pulsation pattern (frequency characteristics) changes when the burner tip position or the air ratio is changed, it becomes possible to control, if desired, the combustion state by means of the pulsation pattern. Based on the predetermined correlation between the frequency characteristics and the combustion characteristics inside a given furnace, such as shown in Table lit is possible to quantitatively estimate the various state of combustion inside the furnace, such as rapid or slow combustion, long or short flame or low NOX or low smoke production, in terms of an objective index, ie the frequency. By feeding back the pulsation pattern to the control system which controlling the combustion state determining factor such as the burner tip position or the air ratio, it is possible to correct the deviation of the combustion from the desired combustion characteristics and to maintain the combustion in a stable and desired state. Hence it is possible to automatically control the combustion state through the quantitative measurement of the furnace condition according to the minute pressure pulsation pattern.

In principle, an ordinary manometer may be used as the instrument for the detection of the minute pressure pulsation pattern inside the furnace. As a practical matter, however, it is preferred to use a pressure transducer using a wire strain gauge as the detector in combination with an amplifier connected thereto. The instrument used is such as to provide a measurable strain value at a pressure of about 20 mm H2O since the minute pressure pulsation pattern inside the furnace is at about 20 mm H2O.

The pulsation pattern may be read out directly by the pressure pattern using a stylus oscillograph. It is however more convenient and more practical to store the pulsation signal in a data recorder connected to the amplifier (dynamic strain gauge), subjecting the signal to a power spectral density analysis and reading out the pulsation pattern on the basis of the resulting frequency characteristic.

A detailed explanation will now be given as to how to reflect the results of determination of the combustion state on the combustion control.

For the purpose of energy saving and the prevention of environmental pollution, a number of factors may generally be used to control the combustion state inside the combustion furnace besides the air ratio, the atomising quantity of the oil burner and the burner position. However, the following explanation will relate to a method and an apparatus for controlling these three factors.

As to the control of the air ratio, it has been confirmed that when the energy level of a set frequency band exceeds a predetermined value, a signal for decreasing the air ratio should be produced in accordance with the deviation and when the former becomes lower than the latter, the air ratio should be increased.

As to the position of the burner, it has been confirmed by various experiments that when the energy level of a set frequency band becomes higher than a predetermined value, a signal should be produced so that the burner position is moved to the right direction in Figure 3 (ie into the inside of the furnace) in accordance with the deviation and when the former becomes lower than the latter, on the contrary, a signal should be produced so that the burner position is moved to the left in Figure 3, that is, towards the throat of the furnace.

As to the atomising quantity of the oil burner, further, it is possible to maintain stable combustion control by producing a signal for reducing the atomising quantity of the oil burner in accordance with the deviation when the energy level of a set frequency band becomes higher than a set value, and by producing a signal for increasing the atomising quantity when the former is lower than the latter.

Examples of the apparatus for controlling these combustion limiting factors are as follows. Figure 22 is a block diagram of the apparatus for measuring the minute pressure pulsation wherein the minute pressure inside the furnace is detected by a detector 9 through a minute pressure pick up probe 8 and its signal is amplified by an amplifier 10. The minute pressure pulsation pattern is determined by a frequency analyser 18 and used as a control signal source. The power spectrum can, for example, be obtained in this manner.

Symbols (a) and (b) in Figure 23 represent respectively a combustion state determination apparatus whereih a filter 18' is provided for passing only signals from a specific band within the broad band frequency components of the minute pressure pulsation to a frequency analyser 18, the frequency analyser 18 being followed by means 18"for using the minute pressure pulsation signal which has been converted into an electric signal by the frequency analyser, as the control signal source. Though only a specific frequency may be picked up by the filter 18' and then fed to the frequency analyser 18, the minute pressure pulsation signal may be applied as an input directly to the frequency analyser 18 and/or to the operator 18" over the whole frequency band.Alternatively, control may be made using both the complete frequency band signal and a specific frequency band signal.

Figure 24 shows a combustion control apparatus in which the output signal from the frequency analyser 18, that is to say, the signal resulting from the analysis, enters a pulsation energy controller 19 and is compared with the value of an energy level of a predetermined frequency or of a predetermined frequency band so that each of the combustion-limiting factors is suitably controlled via a controller 20 and a relay 21 shown respectively in Figures 25, 26, 27, 28, 29 and 30 in accordance with the deviation signal. In the combustion air quantity (air ratio) controller shown in Figure 25, a combustion air quantity valve 14 is disposed while in the cascade type controller shown in Figure 28, there are disposed an automatic variable air ratio setter 38, an air flow controller 39 and an air flow meter 15, in order to adjust and control the air quantity.

Next, Figure 26 shows an atomising quantity controller wherein the atomising quantity is controlled by means of a relay 21 and an atomising flow control valve 23 of the oil burner. Figure 29 shows an apparatus equipped with an automatic variable type atomising ratio setter 26, an atomising flow controller 22 and a flow meter 24.

Figure 27 shows a burner position controller which controls the movement of the burner 3 to a suitable position by means of a burner driving device 30. Figure 30 shows a burner position controller which is equipped with a guide roller 21 and a burner postion control meter 32 in addition to the burner driving device 30.

Though the present invention has been explained with reference to the above mentioned embodiments, the present invention is not particularly limited thereto. For example, the same effect would be obtained by measuring acoustic pressure using a microphone. Alternatively, combustion state limiting factors other than the above mentioned factors may also be controlled. For example, the fuel injection speed from the burner, the air velocity or the pressure inside the furnace may be controlled.

As described in the foregoing paragraph, the present invention has established in the measurement of the combustion state a novel technique capable of accurately estimating the combustion state through a simple operation, ie detecting the minute pressure pulsation superimposed on the pressure inside the furnace, instead of relying, as in the conventional method, on the observation with the naked eye through the inspection hole of the furnace and hence has been of a qualitative nature and of low reliability. (Moreover, there are many commercial furnaces not having an inspection hole itself due to the limitation imposed by the construction of the furnace.) Through this quantitative measurement of the state of the furnace, the present invention has made it possible to properly control the combustion state, to fully automate the combustion control and to eliminate the troublesome procedure of observation with the naked eye and also removes the necessity of the inspection hole for that purpose. Thus, in some circumstances, the present invention has also solved a problem of furnace construction.

Claims

1. A method of determining the combustion state in which the minute combustion pressure pulsation is detected and the combustion state is determined on the basis of this minute pressure pulsation pattern.

2. The method of determining the combustion state as claimed in claim 1 wherein the combustion state is determined on the basis of the energy density distribution obtained by converting the waveform of the pressure pulsation so detected intio a power spectrum.

3. A method of controlling a combustion state limiting factor in the combustion inside a furnace in which the pressure pulsation inside the furnace is detected and compared with a pulsation waveform corresponding to a desired combustion state and the combustion state limiting factor is controlled on the basis of that comparison.

4. The method of controlling a combustion state limiting factor as claimed in claim 3 in which, as the combustion state varies, changes occur in a predetermined frequency band of the detected pressure pulsations which results in corresponding changes in the pulsation energy density detected inside the furnace, this detected pulsation energy density being compared with the predetermined pulsation energy density in said frequency band of the pressure pulsation inside the furnace at a desired combustion state to provide an index in order to control the combustion state limiting factor on the basis of the deviation of the maximum value of the detected energy level in said frequency band at each combustion state from said predetermined value.

5. The method of controlling a combustion state limiting factor as claimed in claim 3 in which as the combustion state varies, changes occur in a predetermined frequency band of the detected pressure pulsations which results in corresponding changes in the pulsation energy density detected inside the furnace, this detected pulsation energy density being compared with the predetermined totai pulsation energy at the most optimum combustion state whereby the ratio of the detected energy density to the total predetermined pulsation energy provides an index to control the combustion state limiting factor on the basis of the deviation of the index from a set value.

6. The method of controlling a combustion state limiting factor as claimed in claims 2,4 and 5 wherein said combustion state limiting factor is a fuel to combustion air quantity ratio (excess air ratio).

7. The method of controlling a combustion state limiting factor as claimed in claims 2, 4 and 5 wherein when a liquid fuel burner is used, said combustion state limiting factor is the quantity of atomised fuel.

8. The method of controlling a combustion state limiting factor as claimed in claims 3,4 and 5 wherein said combustion state limiting factor is the burner tip position.

9. An apparatus for determining a combustion state in a furnace including: means for detecting a minute combustion pressure pulsation inside a furnace caused by the combustion and converting it into an electric signal; means for amplifying said electric signal; and means for analysing the amplified electric signal into its frequency components.

10. An apparatus for determining a combustion state in afurnace including: meansfordetecting a minute combustion pressure pulsation inside a furnace caused by the combustion and converting it into an electric signal; means for amplifying said electric signal; means for analysing the amplified electric signal into its frequency components and comparing them with a predetermined value; and means for adjusting and controlling combustion state limiting factors on the basis of a deviation signal obtained as a result of the comparison.

11. Apparatus for controlling combustion as claimed in claim 10 further including means for adjusting and controlling the combustion air quantity (excess air ratio).

12. Apparatus for controlling combustion as claimed in claim 10 further including, in a liquid fuel burner, means for adjusting and controlling the quantity of fuel atomised.

13. Apparatus for controlling combustion as claimed in claim 10 further including means for adjusting and controlling the burner position.

14. Apparatus for controlling combustion as claimed in claim 10 wherein said means for analysing the amplified signal of the minute combustion pressure pulsation is a frequency analyser having a band pass filter at its input and an operator at its output.

15. Apparatus for controlling combustion as claimed in claim 11 wherein said means for adjusting and controlling the excess air ratio includes a pulsation energy controller, an air flow control valve and an air flow meter.

16. Apparatus for controlling combustion as claimed in claim 12 wherein said means for adjusting and controlling the atomising quantity of the liquid fuel burner includes a pulsation energy controller, an automatic variable type atomising ratio setter, an atomising flow controller, an atomising flow control valve and an atomising flow meter.

17. Apparatus for controlling combustion as claimed in claim 13 wherein said means for moving the burner position includes a pulsation energy controller, a burner driving device, a burner position controller and a guide roller.

18. Apparatus as claimed in claim 9 substantially as hereinbefore described with reference to the accompanying drawings.

19. A method of determining the combustion state as claimed in claim 1 or a method of controlling a combustion state limiting factor in the combustion inside a furnace as claimed in claim 3 substantially as hereinbefore described.