NO318569B1 - Procedure for automatic firing setting of a refuse incinerator - Google Patents

Abstract

For automatically setting the furnace in a waste burning system.

Description

The invention relates to a method for automatic firing setting of a waste incineration plant.

When operating a waste incineration plant, it is important to adapt the burning of the "rubbish quality" in the right way so that the burning is stable and optimal with regard to the emissions. The most important parameters that affect the firing in this case are the flammability and burning properties of the rubbish. As the two factors are not measurable variables, direct measurements are not possible. To date, the applicant has therefore not been aware of any measurement or method that unequivocally determines the "rubbish quality" with regard to fireability and burning properties. Only indirect measurements have been carried out so that the waste incineration setting has been set in advance. As the two aforementioned criteria fireability and burning properties are certainly affected by the rubbish's calorific value and water friction, a method for rubbish burning has been proposed which determines the rubbish's calorific value as early as in the allocation chute. An example of this is the publication DE 44 45 954 Al. This method uses a process control unit to control the amount of combustion air and/or the feed amount of the waste. The calorific value is obtained from measurements carried out using microwaves. Transmitted microwaves are reflected and sent back, as this reflection is used to determine the waste's water content. However, this measurement method has various disadvantages. It is extensive work to install the sensors, and it also entails relatively large costs. In addition, the measurement is only available at discrete points.

The printed publication DE 3537945 A1 also discloses a method for optimal operation of a waste incineration plant which controls the amount of air as a function of the calorific value. In this case, the combustion air can be set in individual zones. This is done continuously to adapt the quantity to a fluctuating calorific value. The calorific value is obtained in this case from the quotient of the current released heat and the waste mass flow. When the air is set, the CO and 02 content of the exhaust gas is also taken into account in the calculation. However, the waste's water content is not included in the calculation by this method, even though it is of decisive importance in an incineration.

Combustion control in waste incineration is also known from "Ent-wicklung einer kameragefuhrten Feuerungsregelung zur Verbes-serung des Verbrennungs-, Ausbrand- und Emissionsverhaltens einer Abfallverbrennungsanlage" (Development of camera-guided combustion control for improving combustion, burning and emissions at a waste incineration plant) , GB Kraftswerkstech-nik 73 (1993), Volume 7. In this method, the O2 concentration in the exhaust gas and the amount of steam generated are determined in order to control the temperature in the furnace in an optimal way with regard to the pollution. The waste charge and the primary and secondary feed are determined by these values, the C0 content being minimized. In this case, the air supply can be adjusted in different zones on the heating grate. This method uses camera monitoring which is used to determine the temperature distribution in the boiler using infrared images. However, this system is relatively complicated and expensive due to the camera surveillance. This method for controlling the firing efficiency of firing furnaces by differentiated feeding of primary air in zones on the firing grate is also described in the printed publication EP 352 620A2.

A method for controlling the combustion of fuel with a highly fluctuating calorific value is disclosed therein

printed publication EP 317 731 Bl. In this case, the water content of the fuel and/or the C02 content of the combustion gases is measured using the prevailing radiation intensity in the area of the charging point and the evaporation and degassing zones in the furnace. These values are used, among other things, to determine the calorific value of the rubbish and on this basis control the air intake. A disadvantage of this previously known technique, however, is that if the rubbish is moist, even the water content and the C02 content in the exhaust gas will decrease due to significantly poorer combustion. In cases of an auto-

However, in terms of fuel management, this will mean that the litter seems significantly drier than it is in reality. In addition, expensive optoelectric sensors are required to detect the water content and/or the C02 content.

The present invention overcomes the above-mentioned disadvantages. It achieves the purpose of providing a method for determining litter quality that works easily and reliably. If an exhaust gas scrubber is used, the method is only intended to measure temperature, pressure and differences (for example, volumetric flow). It is therefore intended to be able to be easily integrated into existing waste incineration plants and to be cost-effective.

According to the invention, this is achieved in a method according to the preamble of the independent claim by the fact that, in order to set the control parameters such as combustion air distribution, litter layer thickness and rupture speed, an artificial "trash quality process parameter is determined from the calorific value of the litter (HU) and the water content of the litter ( H20sappei) •

If the system comprises a flue gas scrubber, a direct measurement of the water content becomes unnecessary according to the method according to the invention. The water formed during combustion can also advantageously be determined via a statistical relationship between the heat of combustion and the carbon mass flow. The procedure can also be integrated into an existing waste incineration plant in a simple and cost-effective way, as almost all the equipment required is already present. Despite the fact that the procedure is simple, it is very reliable.

Further execution possibilities are the subject of the application for the non-independent claims. Figure 1 schematically shows the method according to the invention Late. Figure 2 shows a diagram of the "garbage quality" versus

the calorific value and water fraction of the rubbish,

Figure 3 schematically shows the determination of waste throughput the flow, Figure 4 schematically shows the determination of waste throughput the flow, Figure 5 schematically shows the determination of the water content in

the flue gas.

Figure 6 schematically shows the determination of the water content in the flue gas with temperature measurement upstream of and in the flue gas scrubber, Figure 7 shows the diagram for determining the water content in the flue gas from the flue gas inlet temperature and saturation temperature of flue gases in the scrubber, Figure 8 shows a statistical relationship between the released heat and the carbon mass flow ,

and

Figure 9 shows a diagram of how sensitive the method is

according to the invention is too wrong.

Only the elements that are of importance to the invention are shown. Identical elements are indicated by identical reference symbols in the various figures.

The method according to the invention is suitable for forming a fingered "garbage quality" parameter by determining the HaOuuppei water content values of the garbage and the calorific value of the garbage Hu in a garbage incinerator and thus for making automatic adjustment of the firing, for example with reference to important parameters such as the combustion air distribution, the garbage layer thickness or the shake speed.

Figure 1 shows schematically how the procedure arrives at the values for calorific value (Hu) and waste moisture content

(A). In this case, the waste mass flow is determined

(F garbage) first from the individual garbage crane loads. The calorific value (Hu) of the waste is then calculated via the amount of heat that is transferred by means of the waste mass flow and the amount of fresh steam that is formed. The flue gas moisture content (A) can be

without is determined from physical conditions using temperature measurements, and the waste's water content (A) can be determined from these via the statistical relationship. A litter quality is determined from the calorific value of the litter and the litter moisture content and is used to automatically set the firing. The following measurements or components that are usually present in any waste incineration plant are required to determine the aforementioned values: • Waste crane system with weighing device for the individual, loaded waste batches

• Boiler

• Measurement of the amount of fresh steam

• Temperature and pressure of the fresh steam and feed water

• Volumetric flow of the combustion air

• Either a scrubber with temperature measurements of the flue gases before entering and in the scrubber, or H20 measurements in the flue gas at the boiler end.

In Figure 2, the "rubbish quality" is shown in a three-dimensional diagram with the two basic parameters calorific value and water fraction in the rubbish. The "rubbish quality" is higher the higher the calorific value and the lower the water fraction in the rubbish. The slope in this diagram, which gives the litter quality, has been determined on the basis of experiments and many years of experience. The following steps are carried out in the method according to the invention: 1. Calculation of the garbage flow-en/the garbage mass flow maeppei- Figures 3 and 4 schematically show the first method step in a garbage incineration plant 10 with a furnace 40. To enable a quick calculation of the garbage throughput m8(S!ppei), the throughput is calculated on the basis of the time intervals between the charges and the amount of the garbage charge in a hopper 20 . In this case, it is assumed that the charge volume is constant (= grab charge content 1-12) and that only the specific weight changes. The number of grab charges required to fill the waste chute 50 (determined once) is also known. The grab charges are numbered from 1 to 12 in Figures 3 and 4. This type of waste flow calculation further requires that the filling is more or less always carried out up to an identical mark 30 in the waste chute 50 (for example in a weld, the rounded edge or the visual area of the camera) As a result, the reduction in volume between 2 charges corresponds to a grip charge.

The sequence for determining the garbage g j only the escape m^ppei is as follows: • The garbage chute 50 is filled up to the mark 30, for example with the help of 8 grabs (No. 3-10), • The weight of each of the grab charges is known (stored in process management system) , • The crane operator fills the hopper 20 with a small grab charge in the funnel1 20, • Due to the garbage incineration feed, the garbage slides slowly down the garbage chute 50 until the mark 30 is reached, • At this point the hopper is filled with a new gripping charge (no. 12), • The time tn.12 which the small gripping charge is used to reach the mark 30 (corresponding to the volume reduction) is measured, • The mass w3kg of the gripping charge 3 must have been introduced into the furnace during this time, • Due to the garbage incineration feed slides the garbage slowly down the garbage chute 50 until the mark 30 is left

reached,

• A new grappling charge is filled in the funnel (no. 13),

• The time tu-u which the twelfth gripping charge has taken to reach mark 30 (corresponding to the volume reduction) is measured, and • The mass w4kg of gripping charge 4 must be transported to the furnace during this time.

Rubbish was the only escape during this period via 2 grab charges

To minimize the impact of errors in the assumptions (uniform filling, constant volume, etc.), the average of a few grab loads (depending on grab volume, plant size and crane operator's driving pattern) is taken.

2. Calculation of the waste calorific value Hu.

If the garbage g j only the escape msappeier is known, the garbage calorific value Hu can be calculated using the boiler efficiency Xkjeii the enthalpy of the feed water hssvog the fresh steam hn, in addition to the amount of fresh steam mfdav the garbage calorific value Hu. The waste incineration heat effect is then:

which gives (from a steam table): Fresh steam enthalpy (FD):

Enthalpy of feed water (SPW):

The heating effect supplied when an additional burner is used (for example backup firing for 17th BimSchV):

By using (1) and (2) you get the following expression for the waste burning value:

3. Determination of flue gas moisture content HaCwgaea

The flue gas moisture content helps to determine the water fraction in the rubbish. Due to the lack of suitable measuring systems, the water fraction in the litter cannot be detected directly. The higher the water fraction in the waste, the more water must be evaporated before and during firing. The flue gas moisture content must therefore also increase. This process is shown in Figure 5.

The flue gas moisture content HaOrøkgascan be calculated in the case of an existing scrubber from the flue gas temperature upstream of the scrubber and the saturation temperature in the scrubber. Figure 6 shows this process with the two temperature measurements. The flue gas moisture content HaOnfcgass can be determined using these measurements via a diagram shown in figure 7.

The following applies: the drier the flue gas, the more water it can absorb and the lower the saturation temperature in the scrubber. If you do not have any scrubbers, the flue gas moisture content HaOre,kgafls is determined directly, for example by means of a measurement based on laser absorption (at the appropriate frequency).

4. Calculation of the flue gas volumetric flow Vr^kgass

The volumetric flue gas flow can be calculated using a mass balance where the respective densities are taken into account:

there:

measured parameters: ^ pl^ sl constant parameters: Vfoiski, </ >

Fraction aake = 25%

per kgaoB » 1.277 kg/Nm<3>

calculated parameters (from (1)): msmtl

It is known from various facilities on the basis of approval tests and effect measurements that 20-30% of the waste mass flow is applied as ash mass flow (suspended ash and sawdust) and that it is relatively constant on average.

The flue gas densityPrakgas depends on the composition. The density prsjcgaaa= 1.277 kg/Nm<3> corresponds to the following (average) flue gas composition (percent by volume): 14.5% H20, 11% C02, 7.5% O2, the rest N2.

5. Calculation of the water mass flows rhHi0rfkgaa

The total water mass flow mHi0nlgiaj at the boiler end is calculated using (7) and (8) from:

The water found in the flue gas has 4 different sources:

• Combustion of H in the waste incinerator

• Combustion of H in the additional heating (oil)

• H20 from the combustion air

• H20 from the garbage

which gives:

which in turn gives that By means of a statistical evaluation of the measured data, there were linear relationships

established from approval tests and effect measurements that used an installed C02 measurement in the flue gas. This equation follows from the diagram reproduced in figure 8.

The C mass flow from combustion is calculated from this.

If a constant C/H ratio is used for the waste, the above ratio can also be used to calculate the H20 mass flow from the waste incineration. The C/H ratio is typically 7 to 8. With a constant value of 7.5 for the C/H ratio, the equation gives:

Additional heating with fuel oil provides:

where fraction H is known for different types of fuel oil (fuel oil EL = 13%).

Water introduction via the combustion air provides:

where ^2^j6riremt(p/ii??is between 7 to 12 g/Nm<3>and is assumed to be constant in this range.

6. Calculation of the water fraction in the rubbish

H20 apple

The ratio between the water mass flow rhHi0_ Jtppcl from the litter (11) and the litter flow rhnppel (2) gives the water fraction in the litter:

All calculations are based on constants or assumptions. They give a wrong result with regard to the effective, physical value. The fingered "garbage quality" parameter as a basis for setting the firing is based on these calculated values. However, the absolute values do not play a significant role in waste incineration. When the absolute value changes, however, is of crucial importance. In the final analysis, the setting of the firing is changed using the fictitious "junk quality" variable before the value changes. Systematic errors (due to incorrect assumptions or incorrect constants) that primarily affect the absolute value will therefore not affect the firing process. However, it is the litter mass flow " Ktppei that exerts the greatest influence on the "trash quality" variable of ultimate importance. However, the present procedure is designed so that this influence can be elegantly neglected:

A (small) error in the calculation of the waste mass flow

Mfppeinar the following effect:

Initial situation: Hu = 10,000 kJ/kg and the waste water fraction H2Ottppel= 30% gives a waste quality of 29.2%. If the calculated waste mass flow is approximately 10% greater than the effective value, the calorific value Hu and the water fraction in the waste H2Osvpel will be less than this 10%.

Initial situation error: Hu = 11,000 kJ/kg and the waste water fraction H2<O>aøp<p>el- 33% gives a waste quality of 31.2% (previously 29.2%).

If the water mass flow m,^ from the litter changes by + 10%, this gives a litter quality of approximately 24.6% (previously 29.2%) with a Hu of 10,000 kJ/kg. The quality of rubbish has thus deteriorated.

If the calorific value of the rubbish changes by + 10%, this gives a rubbish quality of 36% (previously 29.2%) if the water fraction in the rubbish is 30%. The quality of rubbish has, of course, improved.

Figure 9 shows in a diagram a few examples of how an error in the waste mass flow m^^, calorific value Hu and water mass flow mH^ 0_ stKia changes with regard to the waste quality. The error can be eliminated entirely from the calculation of the debris mass flow w,^, or at least kept small by a suitable selection of the function

All calculations are based only on

• Temperature measurements

• Pressure measurements

• Differential pressure measurements (throughflow, volumetric flow)

(in those cases a scrubber is used to clean the flue gas). These measurements are also readily available in the field of application for waste incineration. It follows that the fingered "junk quality" process parameter must also be readily available.

Small errors that offset each other or reinforce each other are made in all calculations. However, the present method of determining the "junk quality" which serves as a basis for setting the firing has been shown to be very reliable in various plants regardless of these errors. The fingered "junk quality" process parameter corresponds to the firing condition observed in the furnace below 95 % of all operating cases It follows that the most suitable signal is the signal from a value from which a firing setting can be derived using functions and tables (combustion air distribution, litter layer thickness, grate speed, etc.).

The procedure is understood so that it can be incorporated into any commercially available management system. It does not depend on any additional special equipment or special software.

A calculation example (current image) from a waste incineration plant is given below as an example. The control system recalculates the values directly every 250 ms.

1. Garbage throughput

The grappling charges 3-10 with the masses w3-wl0 are located in the trash-fur hunt:

The grab charge 10 has reached the mark after 10 min, after which a grab charge wll is loaded and then (wll at the mark) a grab charge wl2 is fed: The garbage throughput is calculated at the time 09:25 as

2. The garbage incineration value

hpD«= f (Tfd,Pfd) from water/steam table Tro = 400°C

Ppd <= 39 bar

hm = 3217.4 kJ/kg

hs<p>w = f (TSPW, PSpw) from water/steam table Tspw = 130°C

PS<p>w = 56 bar

hspw = 549.9 kJ/kg

mro ■ 55.000kg/h = 15.2778 kg/s

Shell=0.855

Qadditional belt=0 kW

=>QB = 47.665 kW

3. Flue gas moisture content

HaOrBkgafls<3>f (Tgaaa opstrsmifl the scrubber; Tgaas in the scrubber) •

Believe upstream of the scrubber = 180°C

Saturation temperature of the flue gases in the scrubber = 62°C<=>>H2Flue gas=15.60 VOl% 4. Volumetric flow for flue gas Vpl= 56,500Nm<3>/h

VaL = 11,600 Nm<3>/h

VfaiBlc air=5000 Nm<3>/h

mfflsppei = 14.568 kg/h (see above)

Fraction*^ = 25% ;Prøk gas=1.277 kg/Nm<3>;;82.572 Nm<3>/h ;5. Water mass flows ;<V>volume triac tightening pre-flue gas= 82.572 Nm<3>/h (see Above) ;HaOr^gas=15.60 Vol% ;Prøk gas=0.80 kg/Nm<3>;^Hlo_^^-^CUw , -Ph iO^ =lO,3O5kg/h ;<m>H2o oil - 0 kg/h ;H20 combustion air t = 10 g/Nm<3>;;kc02=0,3770 kg/kWh ;QB = 47,655 kw ( see above) ;6. Water fraction in the garbage ;nisappei = 14568 kg/h (see above) ;<i>%ao garbage = 3739 kg/h ;;7. Waste quality ;H20aBppei — 25.66% ;HuBøppei= 11779 kJ/kg ; ; Qeøppel=55.40% ;LIST OF REFERENCE SYMBOLS ;L_12Grapper content ;20 Hopper ;30 Brand ;40 Firing ;50 Garbage chute ;60garbage incinerator hroFriskdaarpentalpyHgp*Feedwater enthalpy

H20 Water

Calorific value

C<p>roposition factor

^ Mass flow m^ i Garbage mass flow Pro Fresh steam pressure

<p>spw Feed water pressure PL<p>rim air

q heating effect

qBFiring heat outputSLSecondary air

T Temperature

Tfd Fresh steam temperature

TfiPW Feedwater temperature

t Time

V Volume

V volumetric flow of flue gas

smoke gas

WjThe mass of the 3rd grappling charge

W4The mass of the 4th grappling charge

j p Density

^exe The boiler effect

Claims (4)

1. Procedure for automatic firing setting of a waste incineration plant where the waste burning value (Hu) is determined continuously from the heat (QB) which is simultaneously released in the furnace and the input waste mass and the escape (mSøppei) characterized by setting the combustion parameters, such as the combustion air distribution, waste layer thickness and grating speed determines a fictitious "garbage quality" process parameter from the garbage calorific value (Hu) and the water content of the garbage (H2Osøppei), where the water content of the garbage pile (^Ogappei) is determined using the equation where mH2o_sBIipeis the water mass flow of the garbage and water mass t the escape of the garbage mmo sappei is made up of mH20_ s* ppel = mH10_ raligas ~~ mH20_ stppetforbrenntng ~ mH1O oil ~^ HiO_ combustionthfP der<=>mH2o_røicgasser the water mass flow i flue gas - m H2o_Bøppeiforbrecning is the water mass flow that is formed during combustion, "»H2o_oije is the water mass flow which is formed during the additional oil firing, and wH2o_forbrenningsiuft is the water mass escape in the food combustion air, in which case one gets that: there Vrrt& istWendtn is <*a volumetric flow of the flue gas at the boiler end, I^OrekgMs is moisture content in smoke the gas, pHjO_ steam is the density of the water in the form of steam, there will be a proposal for the prosecutor and QB is the heat released below firing, =Moije fraction,, -9,000 where m^ e is the mass flow of the oil and fraction Here the fraction of hydrogen i the oil, where VPL is the volumetric flow of the primary air, is the volumetric flow of the secondary air, Jj&irt/ijf? is <*a volumetric flow of the false air, and #20**™**,** is water present in the air fed to the combustion 2. Method according to claim 1, characterized in that the moisture content in the flue gas (H20rBkgB„) is measured directly at the boiler end. 3. Method according to claim 1, characterized in that the moisture content in the flue gas (H2OrakgagB) is determined from the temperature upstream of the entrance of the flue gas to a flue gas scrubber located downstream of the waste incineration plant, and from the saturation temperature of the flue gases in the flue gas scrubber. 4. Method according to one of claims 2 or 3, characterized in that the proportionality constant, k^o, is determined by a statistical relationship between carbon dioxide mass flow mæl= Km2<*>QB and the carbon-to-hydrogen ratio (C/H) in the waste, k^ is the proportionality constant between the liberated heat (QB) and the carbon dioxide mass expansion ( fh coa ).