NL1012798C2 - Method for determining the oxygen requirement for burning a fuel, method for burning a fuel and device therefor. - Google Patents

Description

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Method for determining the oxygen requirement when burning a fuel, method for burning a fuel and device therefor

The present invention relates to a method for determining the oxygen requirement when burning a fuel.

Such a method is known from practice.

The known method is usually carried out by measurements in a combustion device, whereby a known amount of fuel is burned per unit of time and the consumption of gaseous oxygen is measured by measuring the oxygen concentration in flue gas with the aid of an oxygen concentration meter.

A drawback of the known method is that it takes a long time and is inaccurate due to the slow reaction of the device to a new fuel.

The present invention aims to provide a method with which a precise value for the oxygen requirement when burning the fuel, such as a fuel of an unknown or variable composition, can be determined relatively quickly.

To this end, the method according to the present invention is characterized in that a predetermined amount of the fuel is contacted with an inert liquid containing a predetermined excess of oxidizer, the fuel being oxidized by the oxidator, after which i) the amount remaining after oxidation Oxidizer is measured, * or ii), if the oxidizer produces a reducing agent upon reaction with the fuel, the amount of reducing agent or oxidizing agent is measured; from which quantity values of the oxidizer or reducer a value for the oxygen requirement is derived.

30 Thus, the oxygen requirement of a variety of solid or liquid fuels, or solid or liquefied fuels including i) mineral fuels such as petroleum, and products thereof such as plastics and ii) biomass of various origins, such as pruning waste, may exceed 4 Λ ao “ 9 λ «k 'j 2 non-composted vegetable, garden and fruit waste, thinning wood and wood grown for energy-generating purposes, demolition, residual and waste wood are determined. The method according to the invention measures the consumption of oxidizer in a "wet chemical" manner; a predetermined amount of fuel is brought into a solution containing an excess of a chemical oxidant. After the reaction, the amount of the remaining oxidant or the resulting reducer is determined wet chemically (titration). The required amount of oxidant is then converted arithmetically into the amount of oxygen consumed. Such a measurement based on weighting and titrimetric determination is very accurate. In the present application, an inert liquid is understood to mean a liquid which cannot be oxidized by the oxidizer under the reaction conditions used.

The invention is in particular also suitable for those fuels which, upon combustion, yield a solid residual. For example, it is known to use paper sludge or waste paper as fuel to yield a solid residual material which, under suitable process conditions, yields a usable product, as described in European patent 0,796,230. The varying composition necessitates adequate determination of the oxygen requirement for good control of the process conditions. Therefore, according to a preferred embodiment, the fuel is paper sludge or waste paper.

According to a favorable embodiment of the method according to the invention, the value of the oxygen requirement is used for determining the calorific value of the fuel.

It has been found that there is a direct relationship between the oxygen consumption measured according to the invention and the fraction of organic material in the fuel. Furnace builders usually have correlations between the fraction of organic material in the fuel and the energy content of the fuel (the calorific value) for a particular fuel, based on experience. For known fuels with a variable content of incombustible material (such as paper sludge containing a variable content of clay), using the method according to the invention and the knowledge of the oxygen consumption for 100% organic material, the fraction organic can be used. material are determined. The calorific value can be calculated from this. Due to the above correlation, the calorific value can also be determined directly from the oxygen consumption, as will be shown below.

The present invention therefore also provides a favorable method for determining this quantity which is important for both the design and the operation of incinerators.

In order to determine the calorific value, it is known to use a bomb calorimeter. The fuel is here brought together with an excess of oxygen into a vessel (the "bomb"), after which the fuel is ignited. The bomb is placed in an energy-absorbing medium, the temperature rise of which is measured and thus the energy released during combustion can be determined. However, particularly with fuels containing a solid residual (such as calcium carbonate), mineralogical conversions occur which are not necessarily the same as those occurring under the combustion conditions with the fuel in the combustion apparatus. Since a mineralogical conversion is accompanied by an enthalpy change, this causes inaccuracies in the determination of the oxygen requirement on the basis of thermal measurements. The present invention avoids this problem.

According to another favorable embodiment of the method according to the invention, the oxygen requirement is determined by measuring the chemical oxygen demand (COD). Determination of the chemical oxygen demand (En gels: COD, Chemical Oxygen Demand), such as according to the Dutch standard NEN 6633, is a generally known method, which is used for determining the contamination of waste water and the like. This simple assay involves boiling the assay sample in a strong sulfuric acid medium in the presence of silver sulfate and mercury (II) sulfate with an excess of potassium dichromate and then determining the amount of potassium dichromate consumed by titrimetrically. To determine the oxygen demand of a fuel which is not oxidizable under these conditions, it can be subjected to a pretreatment, such as chemical reactions aimed at making the oxidizing components in the fuel for oxidising agent more readily accessible. This may include ring-opening reactions, which have been described in the standard organic literature. Furthermore, consideration can be given to halogenation (also described in the standard literature of organic chemistry) which aims to improve the solubility of the components to be oxidized. Furthermore, addition of surfactants which can also improve the solubility of the substances to be oxidized can be considered. The use of these pretreatment methods requires subsequent correction for the possible oxygen consumption of the organic components used in these substances. Preferably, no organic pre-treatment agents are used, so that the correction and any associated measurement error remains minimal.

The present invention also relates to a method of burning a fuel in which oxygen is supplied for maintaining the combustion, characterized in that the supply quantity of the oxygen relative to the quantity of fuel is controlled depending on the oxygen requirement. 25 of the fuel determined value.

The process conditions can hereby be efficiently optimized.

Also, if it is legally required to maintain a certain residual concentration of oxygen in the waste gases, such a residual concentration can be adjusted very accurately by means of the method according to the invention. This prevents an excess of oxygen (i.e. significantly more than the legally required residual oxygen concentration) from being used.

The present invention also relates to a device for burning a fuel with oxygen supply, characterized in that the device is dimensioned in dependence on the value for the oxygen requirement as determined by the method 101P7Qft *> 5 according to the invention.

As a result, a device need not be sized larger than necessary. This limits the investment costs, while also saving the operating costs, since the use of the minimum amount of oxygen required has the result that the costs of supplying it remain limited. If desired, abrasion as a result of entrained solid residual particles and thus wear and tear of the installation can also be limited, by avoiding an excessive flow rate.

The invention will be explained in more detail below with reference to a number of exemplary embodiments and the drawing in which

Pig. 1 the oxygen consumption values determined by the method according to the invention (gram O2 / kg paper residue) are compared with the measured and converted amount of organic material (g organic fraction / kg paper residue).

Pig. 2 shows the 02 consumption (g / kg) of different reference materials plotted against their energy content;

Fig. 3 shows a comparison between the theoretical and actual measured oxygen consumption values for mixtures of some organic compounds mixed with a filler.

25

Example 1

The oxygen requirement is determined from a paper residue stream from a paper mill (dry matter fraction contains approximately 40% organic fraction, 30% clay and 30% chalk). For this purpose use is made of a determination for the chemical oxygen consumption according to the Dutch standard NEN 6633. Briefly, 1 to 5 g of a representative sample, whether or not dried, is taken from the paper residue and suspended in 900 ml of water. 10 ml of the suspension thus obtained is taken and added to a potassium dichromate-containing sulfuric acid solution. Cook gently for 2 hours. The size of the excess potassium dichromate is determined by titration with ammonium iron (II) sulfate solution using o-phenanthroline as an indicator.

1012798 * »6

Instead of a color change, an (automated) Redox measuring device can also, and preferably, be used. From this, the oxygen requirement (based on the amount of sample analyzed) can be determined. As 5 below, it will be indicated how the calorific value can be determined therefrom.

By way of illustration, a specific determination of a model compound is described here (A in Table I). 1.0070 g of glucose (C6H120s * H20 with a dry matter content of 90.9%; 10 Merck) is dissolved in 900 ml of water, yielding solution A. Since glucose can be easily dissolved, in contrast to a paper residue determination no need to stir vigorously to form a suspension. 10 ml of a 0.040 M potassium dichromate solution to which a spatula of mercury sulfate (approx. 0.5 g) and 5 glass beads are added are placed in a rendering tube (Behrotest type TRS 2000, Behr Labor-15 technik, Warsaw, Poland). . 10 ml of solution A is placed in the destruction tube together with 10 ml of water. Then 30 ml of silver sulfate-containing sulfuric acid (10 g of silver sulfate per liter of sulfuric acid) are added. The destruction tube is equipped with a cooler and the destruction tube is placed in a rendering block preheated to 150 ° C and the solution is gently boiled for 2 hours. After partial cooling of the solution in the rendering tube, the solution is made up to 100 ml with water. After further cooling to ambient temperature, titration is carried out with an ammonium iron (II) sulphate solution (approx. 0.14 M). The tipping point of the titration is determined by measuring the electrode voltage jump between 1000 and 700 mV using a Schott 15 Pt 5901A micro-dox glass electrode (Schott Benelux B.V., Tiel, The Netherlands). The exact tipping point is determined by the position of the strongest decrease in electrode voltage.

The oxygen requirement is calculated with the following formula 3 5.

0.5 M

COD = (V2 - V3) C - V! 40 1012798 7 where: COD is the chemical oxygen demand, in mg oxygen per liter Vl is the quantity of water that is being processed: 20 ml 5 V2 is the quantity of iron (II) ammonium sulphate solution consumed in the blank determination: 16.88400 ml V3 is the quantity the determination of the amount of iron (II) ammonium sulphate solution consumed: 8.21236 ml c is the concentration of the iron (II) ammonia used

10 µm sulfate solution: 0.1448 M

M is the atomic mass of oxygen: 16,000 mg / mol.

It follows that the found value for chemical oxygen demand is 502.4 mg 02 / l. 1 Liter of solution Vx 15 contains (1000 ml / 20 ml) * (10 ml / 900 ml) * (1.0070 * 0.909) g of glucose = 0.508 g. The oxygen consumption for glucose is therefore 502.4 mg / 0.508 g = 988 mg O2 per gram of glucose (hydrated). It can be seen from Fig. 2 that the energy content is 12.6 MJ / kg. This corresponds well with the value determined on the basis of the element composition known for this substance with the formula of Dulong (12.9 MJ / kg).

Fig. 1 shows the results in a graph plotting the measured oxygen consumption (grams O2 / kg paper residue) against the measured and converted amount of organic material (g organic fraction / kg paper residue). Figure 1 shows that the method according to the invention correlates well with the directly measured values.

Fig. 2 shows the 02 consumption (g / kg) of different reference materials plotted against their energy content (MJ / kg) 30. The figure shows that there is a direct relationship between the measured amount of oxygen consumption and the energy content of the fuel.

Example 2 Fig. 3 shows the theoretical oxygen demand (g

Oz / kg) plotted against the measured oxygen consumption (g 02 / kg) for three compounds, namely glucose, potassium hydrogen phthalate and citric acid mixed with clay and / or chalk. This shows that the measured amount of oxygen consumption, 101? 7Öft • · 8 as determined according to the present invention, correlates well with the amount of oxygen consumption that is used for the samples shown in this figure 3 (pure glucose, clay and chalk in various mixing ratios, see table 1 below) 5 can predict theoretically. The theoretical values are calculated on the basis of the measured value for 100% pure substance. In other words, this shows that substances such as clay and chalk that interfere with other processes have no influence on the determination of oxygen demand.

10 TABLE 1

Mixture Glucose Chalk Clay theor. COD measured

No. (%) {%) (%) (g 02 / kg) COD

_ | LJg_02Ag) __ | A__100__0__0__881__898_ 15 _B__0__100__0__0__4_ C__0__0__100__0__0_ _D__25__37,5__37,5__220__229_ _E__25__75__0__220__231_ F__25__0__75__220__226_ 20 G_ 50 25__25___440

Claims (6)

1. A method for determining the oxygen requirement when burning a fuel, characterized in that a predetermined amount of the fuel is contacted with a predetermined excess of oxidizer in an inert liquid, the fuel passing through the oxidator is oxidized, after which i) the amount of oxidizer remaining after oxidation is measured; or (ii) where the oxidizer produces a reducing agent upon reaction with the fuel, the amount of reducing agent or oxidizer is measured; from which quantity values of oxidator or reducer a value for the oxygen requirement is derived. Method according to claim 1, characterized in that the fuel is paper sludge or waste paper. 3. Method according to claims 1 and 2, characterized in that the value of the oxygen requirement is used for determining the calorific value of the fuel. Method according to claim 3, characterized in that the oxygen requirement is determined by measuring the chemical oxygen demand (COD). 5. A method of burning a fuel in which oxygen is supplied for maintaining the combustion, characterized in that the supply quantity of the oxygen relative to the quantity of fuel is controlled in dependence on the oxygen requirement according to one of the claims 1-4 determined value. 6. Apparatus for burning a fuel with oxygen supply, characterized in that the apparatus is dimensioned in dependence on the value for the oxygen requirement as determined by the method 30 according to any one of claims 1 to 4. 101279%