GB2484461A

GB2484461A - Fuel containing urban sewage sludge

Info

Publication number: GB2484461A
Application number: GB1016737.7A
Authority: GB
Inventors: Georg Szczendzina; Tobias La Hr
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-10-05
Filing date: 2010-10-05
Publication date: 2012-04-18
Also published as: US20130247458A1; WO2011134808A1; GB201016737D0; EP2563884A1

Abstract

The invention relates to a fuel system and to a process for the production of such a fuel system by using urban sewage sludge. Environment protective energetic use of urban sewage sludge and the reduction of fossil carbon dioxide are the important goals. The fuel system shows a content of fossil carbon which is clearly reduced compared to that of fossil fuels while the fuel-technological properties are the same. Thus the emission of the carbon dioxide based on fossil carbon is notably reduced during the use of the fuel system according to the invention. In one embodiment of the invention, the fuel system is provided consisting of different fossil regular fuels (e.g. brown coal, black coal or anthracite) and urban sewage sludge as biogenic carbon donor, with biomasses serving as a biogenic carbon donor.

Description

Fuel system and process for its production for environmental protective energetic use of urban sewage sludge The present invention relates to a fuel system and to a process for the environmental protective energetic use of urban sewage sludge.

Fuels generally serve as an energy carrier in the production of heat or electric current. From prior art, a number of different fuels are known among which the so-called fossil fuels predominate.

Hard coal, brown coal, lignite, turf, natural gas and petroleum are part of the fossil fuels.

Fossil fuels have been exploited already since the 18th and 19th centuries, and they were considered as the basis for the Industrial Revolution. Particularly during the past 40 years, the worldwide energy demand and hence the consumption of fossil fuels have increased to such an extent that the production of energy from fossil fuels has caused environmental problems.

Fossil fuels are generally based on organic carbon compounds which release energy in the form of heat during the oxidative conversion with oxygen, as this takes place during combustion. Carbon dioxide and water is generated as a byproduct of this oxidative conversion.

Since carbon dioxide which is released during the combustion of fossil fuels originates from carbon compounds that have been stored over millions of years, this massive combustion results in the enrichment of the earth's atmosphere with carbon dioxide.

On the other hand, this carbon dioxide is frequently referred to as a so-called "greenhouse gas" which could contribute to disturbing the ecological balance on the earth. Carbon dioxide in the atmosphere is suspected to reduce the radiation of heat energy from the earth to the universe just as the glass roof of a greenhouse while the incidence of the sun's radiation on the earth is reduced only little. This effect is suspected to lead to global warming.

For controlling the emission of CO2 to the atmosphere, climate-protection goals have been fixed by the European Union in consideration of the Kyoto Protocol, and in this connection there have even been introduced so-called Emission Certificates. Since 2005, the EU membership states are obliged by the EU Emissions Trading Directive to hand in a National Allocation Plan each time at the beginning of an emissions trading period. This plan fixes an amount of greenhouse gases each bigger emitter of a country is allowed to emit within a particular period. Article 9 of these Directives provides the examination and approval of this Allocation Plan by the EU Commission on the basis of 12 criteria. This concerns above all the compatibility of a country's own goals within the scope of the Kyoto Protocol, equal treatment of enterprises and the observance of the EU competitive law. If a company's emission exceeds the allowance that has been allocated to it, the company has to buy additional emission rights from another company. This can be done for instance at the Energy Exchange EXXA. On the other hand, if a company emits less than the allowance that has been allocated to this company, it may sell excess amounts of emission to other companies. However, for in fact reducing the fraction of CO2 in the atmosphere, the allowed emissions are reduced step by step.

Major emitters of CO2 are branches in industry and economy having a high energy demand. These are for instance power plants, petroleum refineries, coking plants, iron and steel works, the cement industry, glass industry, lime industry, brick industry, insulation material industry, ceramic industry, and cellulose and paper industry.

One way for avoiding the accumulation of 002 in the atmosphere is the use of the so-called regenerative energy. In general, these are wind power, water power, solar power, and the use of biomasses as a fuel or for the production of bio gas. However, if biomasses are used as an energy carrier, the problem exists that these biomasses have a clearly lower energy content compared to fossil fuels. On the other hand, biomasses have the advantage that they are extracted as an energy carrier from the current carbon cycle. This means, that on a scale of Earth history, carbon dioxide which is released as a result of the oxidative conversion of biomasses was generated only a short time ago and is also directly extracted again from the carbon cycle by the regrowing plants, if the biomasses are simultaneously planted again. Thus, a carbon dioxide balance is achieved and the accumulation of carbon dioxide in the atmosphere is avoided.

However, due to their clearly lower energy content, fuels based on biomasses as known from prior art cannot be used up to present with sufficient efficiency in the big industry. Moreover, the use of biomasses as a fuel requires fuel technologies which are different from those employed in the combustion of fossil fuels such as black coal or lignite for instance. This means, that the release of a defined amount of energy would require the combustion of a clearly higher amount of biomasses than of fossil fuels on one side and that the use of biomasses as a fuel on an industrial scale would require an expensive modification of already installed fueling systems on the other side.

Apart from their energy content, biomasses which are used as a fuel are different from fossil fuels also with regard to further properties such as ash content, volatile matters, hydrogen content and water content. But all these factors play an important part in the industrial use of fuels in dependence of the respective application, so that frequently it is not possible to exchange fossil fuels for biomasses as a fuel in the field of industrial applications.

The invention is therefore based on the o b j e c t of providing a fuel which is ecologically more favorable on one side and which can be unlimitedly exploited for industrial applications on the other side. It is also an object of the present invention to provide a process for the production of such a fuel.

Concerning the fuel, this object is a c h i e v e d by a fuel system which is characterized in that it consists of a mixture of at least two different fossil regular fuels and urban sewage sludge as a biogenic carbon donor, wherein the amount of the urban sewage sludge is at least 10 % with respect to the total weight.

According to the invention, urban sewage sludge is used as a biogenic carbon donor. In the meaning of the invention urban sewage sludge refers to the residual, semi-solid material left from urban wastewater or sewage treatment processes.

In a preferred embodiment according to the invention, the urban sewage sludge used as biogenic carbon donor is the product anaerobic digestion of raw sludge, for example in so called Imhoff tanks, also referred to as biosolids.

In another preferred embodiment according to the invention, the sewage sludge is raw sludge coming from the sedimentation tank or settling tank of urban sewage plants.

Fossil regular fuels which are preferably used in the fuel system according to the invention are brown coal, black coal, and anthracite. Examples of such usable coals are hard coal, fat coal, gas coal, long-flame coal, bituminous coal, pre-dried black lignite or pre-dried dull brown coal.

In a preferred embodiment of the inventive fuel system, the first fossil regular fuel has a vitrinit reflection Rm of> 2.0, whereat the second regular fuel has a vitrinit reflection Rm between of 0.4 to 2.0.

The vitrinit reflection Rm gives an information about the maturity and the calorification of the fossil regular fuel used. Furthermore, the vitrinit reflection is associated with the combustion behaviour of the deployd fossil regular fuel so that an optimization of the combustion behaviour of the fuel system is possible by choosing fossil regular fuels having a vitrinit reflection parameter within the specified range. Thereby, the combustion behaviour of the inventive fuel system can be adapted to the combustion behaviour of pure fossil fuels, like they are typically used in e.g. powerplanes, whereat as combustion behaviour in particular the fuel value, the calorific value, as well as the ash residue should be understood.

This enables the use of the inventive fuel system in existing firing systems without further plant specific modification. Hence, the inventive fuel system enables an ecological optimization of the firing systems without the need to make plant specific modifications.

According to a further embodiment of the inventive fuel system, at least three fossil regular fuels are used, whereat one having a vitrinit reflection Rm > 3.0, a second having a vitrinit reflection Rm within the range of> 2.0 and 3.0, and the third has a vitrinit reflection Rm within the range of 0.4 and 2.0.

This further embodiment of the inventive fuel system enables in particular an adaption of the hardgrove index, so that the fuel system can be adapted with respect to this parameter to the plant specific conditions, like e.g. coal mills, too.

In a further embodiment of the inventive fuel system, the fuel system comprises beside the fossil fuel and the biogenic carbon carrier a refining product of the group consisting of coke, petrol coke, lignite coke, and charcoal.

In general, there are three different procedures to produce the inventive fuel system: Procedure 1: The urban sewage sludge is putrefied, drained and dried and then mixed with the at least two different fossil regular fuels; Procedure 2: The urban sewage sludge is mixed with at least two different fossil regular fuels and then putrefied, drained and dried; Procedure 3: The urban sewage sludge is mixed with one of the at least two different fossil regular fuels, putrefied, drained, dried, and then mixed with at least one further fossil regular fuel.

The fuel system according to the invention provides a fuel which meets the requirements of fossil fuels concerning its fuel-technological properties while showing a clearly lower emission of CO2 from fossil carbon carriers, based on the releasable energy content.

Thus, the fuels system shows an effective content of fossil carbon which is reduced by at least 11% compared to fossil fuels, referred to the calorific value, with the percentage of fossil fuels being put in a relation to the calorific value for calculating the effective content of fossil carbon.

The content of the fossil carbon in the inventive fuel system can be determined, for example by one of the radio carbon method, also referred to as 14C-method, and the method of selective dissolution.

The 14C-method is a radiometric dating method that uses the naturally occurring radioisotope carbon-i 4 (14C) to determine the age of carbonaceous materials up to about 58,000 to 62,000 years. Raw, i.e. uncalibrated, radiocarbon ages are usually reported in radiocarbon years "Befor Present" (BP), "Present" being defined as 1950. The year 1950 was chosen because it was the year in which calibration curves for radiocarbon dating were first established. 1950 also predates large scale atmospheric testing of nuclear weapons, which altered the global ratio of carbon-14 to carbon-i 2, the naturally most frequently occurring carbon isotope.

When plants fix atmospheric carbon dioxide (C02) into organic material during photosynthesis they incorporate a quantity of 14C that approximately matches the level of this isotope in the atmosphere. After plants die or they are consumed by other organisms for example, by animals, the 14C fraction of this organic material declines at a fixed exponential rate due to the radioactive decay of 140. Comparing the remaining 140 fraction of a sample to that expected from atmospheric 140 allows the age of the sample to be estimated.

Since coal, like other fossil fuels, is the product of carbonization of plants in former geological eras, the 14C-content of fossil and biogenic carbon sources significantly differs, thereby allowing to discern between both.

When using the method of selective dissolution the probe to be examined on its biogenic carbon content is subsequently treated with sulfuric acid and hydrogen peroxide. While the biogenic carbon is soluble in the at least one of the mentioned solvents, fossil carbon is not. As a result the probe is depleted from biogenic carbon. Accordingly by determination and comparison of the total carbon content of the fossil fuel prior and after depletion, the amount of biogenic carbon can be determined. The determination of the total carbon content may be performed, e.g. by determination of the ash content. Also this method allows to discern between carbon coming from fossil and biogenic carbon sources.

Concerning the process, the object of the invention is achieved by a process for producing a fuel system of the above-described kind, comprising the steps of: 1. selecting a first fossil regular fuel having a low content of volatile matters, and a vitrinit reflection Rm > 2.0, a second fossil regular fuel having a medium content of volatile matters, and a vitrinit reflection Rm between 0.4 and 2.0; 2. mixing the first fossil regular fuel with the second fossil regular fuel; 3. mixing the mixture obtained in step 2 with the sewage sludge; wherein in Step 3 at least 10 % by weight, with respect to the total mass of the fuel system, of the sewage sludge is admixed to the mixture obtained in step 2; or 1. selecting a first fossil regular fuel having a low content of volatile matters, and a vitrinit reflection Rm > 2.0, a second fossil regular fuel having a medium content of volatile matters, and a vitrinit reflection Rm between 0.4 and 2.0; 2. mixing one of the selected fossil regular fuel with the sewage sludge; 3. mixing the mixture obtained in step 2 with the other selected fossil regular fuel, wherein in Step 2 at least 10 % by weight, with respect to the total mass of the fuel system, of the sewage sludge is admixed with one of the selected fossil regular fuel.

The selected fossil regular fuel can be admixed to the sewage sludge prior or past putrefying, draining, and drying of the sewage sludge. This means, the fossil regular fuel according to the inventive method may be added to the sewage sludge, for example in the settling tank, sedimentation tank, or the vessel the anaerobic digestion takes place (e.g. an lmhoff tank). When admixing at least one of the selected fossil regular fuel to the sewage sludge prior to putrefying, draining, and drying the sludge, the regular fossil fuel beneficial can act as a filtration additive improving the draining of the sludge.

The mixture obtained by the inventive method may be mixed further with regular fuels. Suitable regular fuels are, for example coke, petrol coke, lignite coke, and charcoal.

The fuel system according to the invention which has been obtained by a process according to the invention is particularly suitable for power plant fuelling in electric power and heat production, for paper production, for the production of glass and mineral melts, and the cement production.

The fuel system according to the invention and the process for its production are described in the following by way of examples which are not in any way limiting to the invention.

In the following table 1, examples of the main characteristics of different fossil fuels and biogenic carbon carriers are shown.

Example I

Table I

Mixture Mixture Mixture Mixture NB/C in % A/BIC in % A/B/C in % NB/C in % by weight by weight by weight by weight Coal A Coal B urban 33/33/33 40/30/30 50/20/30 70/20/10 sludge C Rm vitrinite ref ection 2,8 1,2 parameters (raw, ar) water % 5,00 9,01 25,91 13,31 12,48 12,08 7,89 ash% 7,60 20,50 27,03 18,38 17,30 16,01 12,12 volatile matters % 5,70 21,26 43,47 23,48 21,70 20,14 12,59 sulfur% 0,80 0,93 0,12 0,62 0,64 0,62 0,76 hydrogen % 2,48 3,05 3,31 2,95 2,90 2,84 2,68 carbon total % 78,85 57,85 23,92 53,54 56,07 58,17 69,16 ncvJ/g 29.708 21.833 5.922 19.154 20.210 20.997 25.754 ncvcal/g 7.096 5.215 1.414 4.575 4.827 5.015 6.151 Cfoss % 78,85 57,85 4,48 47,71 50,24 52,34 67,21 Cbiogen % 0,00 0,00 19,44 5,83 5,83 5,83 1,94 ar = as received, ncv = net calorific value A mixture auf coal A and coal B was mixed with urban sewage sludge dry in the ratios mentioned in table 1 according to procedure 1(i.e. the urban sewage sludge is putrefied, drained and dried and then mixed with the at least two different fossil regular fuels) in a mixing drum, until a homogeneous mixture was obtained. In the analytical examination the obtained mixture showed a water content, an ash content, a volatile material fraction, a sulfur content, and a total carbon content as mentioned in table 1. The biogenic carbon concentration was in the range of between 1.94 and 5.83 % by weight of the total mass.

Accordingly, the fuels system shows an effective content of fossil carbon which is reduced by at least 1.94 % to about 6 % absolute compared to fossil fuels, referred to the calorific value, with the percentage of fossil fuels being put in a relation to the calorific value for calculating the effective content of fossil carbon.

The obtained mixture showed a ncv Hu of 4785 cal/g.

The obtained mixture showed an excellent combustion behavior and could be combusted in a stoker-fired furnace previously operated with fossil fuels, without any modification of the installation.

ExamQle 2

Table 2

Mixture Mixture Mixture Mixture NB/C in % NB/C in % NB/C in % NB/C in % by weight by weight by weight by weight Coal A Coal B urban 33/33/33 40/30/30 50/20/30 70/20/10 sludge C Rm vitrinite ref ection 2,8 1,2 parameters (raw, ar) water % 5,00 9,01 10,00 8,00 7,70 7,30 6,30 ash% 7,60 20,50 23,74 17,28 16,31 15,02 11,79 volatile matters % 5,70 21,26 52,81 26,59 24,50 22,95 13,52 sulfur% 0,80 0,93 0,15 0,63 0,64 0,63 0,76 hydrogen % 2,48 3,05 4,02 3,18 3,11 3,06 2,75 carbon total % 78,85 57,85 38,16 58,29 60,34 62,44 70,58 ncv J/g 29.708 21.833 9.992 20.511 21.431 22.218 26.161 ncvcal/g 7.096 5.215 2.387 4.899 5.119 5.307 6.249 Cfoss% 78,85 57,85 20,60 53,02 55,08 57,18 68,83 Cbiogen % 0,00 0,00 17,56 5,27 5,27 5,27 1,76 ar = as received, ncv = net calorific value, A mixture auf coal A and coal B was mixed with urban sewage sludge dry in the ratios mentioned in table 2 according to procedure 2 (i.e. the urban sewage sludge is mixed with at least two different fossil regular fuels and then putrefied, drained and dried) in a mud basin, until a homogeneous mixture was obtained.

The mixture takes place in an urban sewage plant. In the mud basin the sewage sludge is mixed with a mixture of coal A and coal B by simply adding the coal mixture to the mud basin and using the basins agitator to obtain a homogeneous mixture. Afterwards the mixture is drained by reducing of water.

The admixing of the coal to the raw sewage sludge improves the necessary drainage of the sewage sludge.

In the analytical examination the obtained mixture showed a water content, an ash content, a volatile material fraction, a sulfur content, and a total carbon content as mentioned in table 2. The biogenic carbon concentration was in the range of between 1.76 and 5.27 % by weight of the total mass. Accordingly, the fuels system shows an effective content of fossil carbon which is reduced by at least 1.76 to about 6 % absolute compared to fossil fuels, referred to the calorific value, with the percentage of fossil fuels being put in a relation to the calorific value for calculating the effective content of fossil carbon. The obtained mixture showed a ncv Hu of 4522 cal/g.

Claims

Patent Claims 1. Fuel System, characterized in that the same consists of a mixture of at least two different fossil regular fuels and urban sewage sludge as a biogenic carbon donor, wherein the amount of urban sewage sludge is at least 10 % with respect to the total mass.
2. Fuel system according to claim 1, wherein this system includes brown coal, black coal and/or anthracite as a fossil regular fuel.
3. Fuel system according to claim I or 2, wherein one fossil regular fuel has a vitrinit reflection Rm > 2.0, and the second fossil regular fuel has a vitrinit reflection Rm between 0.4 and 2.0.
4. Fuel system according to one of the claims 1 to 3, wherein the same comprising at least three different fossil regular fuels, wherein one fuel has a vitrinit reflection Rm > 3.0, a second as a vitrinit reflection Rm between > 2.0 and 3.0, and a third has a vitrinit reflection Rm between 0.4 and 2.0.
5. Fuel system according to one of the claim 1 to 4, wherein the urban sewage sludge used as biogenic carbon donor is the product anaerobic digestion of raw sludge.
6. Fuel system according to one of the claim 1 to 4, wherein the urban sewage sludge used as biogenic carbon donor is raw sludge coming from the sedimentation tank or settling tank of urban sewage plants.
7. Fuel system according to one of the claims I to 6, wherein this system includes a refinement product from the group consisting of coke, petroleum coke, brown coal coke and charcoal.
8. Process for producing a fuel system according to one of the claims 1 to 7, said process comprising the steps of: 1. selecting a first fossil regular fuel having a low content of volatile matters, and a vitrinit reflection Rm > 2.0, a second fossil regular fuel having a medium content of volatile matters, and a vitrinit reflection Rm between 0.4 and 2.0; 2. mixing the first fossil regular fuel with the second fossil regular fuel; 3. mixing the mixture obtained in step 2 with the sewage sludge; wherein in Step 3 at least 10 % by weight, with respect to the total mass of the fuel system, of the sewage sludge is admixed to the mixture obtained in step 2; or 1. selecting a first fossil regular fuel having a low content of volatile matters, and a vitrinit reflection Rm > 2.0, a second fossil regular fuel having a medium content of volatile matters, and a vitrinit reflection Rm between 0.4 and 2.0; 2. mixing one of the selected fossil regular fuel with the sewage sludge; 3. mixing the mixture obtained in step 2 with the other selected fossil regular fuel, wherein in Step 2 at least 10 % by weight, with respect to the total mass of the fuel system, of the sewage sludge is admixed with one of the selected fossil regular fuel.
9. Process according to claim 8, wherein the selected fossil regular fuel is admixed to the sewage sludge past putrefying, draining, and drying of the sewage sludge.
10. Process according to claim 8, wherein at least one selected fossil regular fuel is admixed to the sewage sludge prior putrefying, draining, and drying of the sewage sludge.