| Claims 1 . The method of use of inorganic fractions from the sewage sludge containing transition metals, characterised in that pre-dried excess water or sewage sludge containing from 5 wt.% to 95 wt.% of transition metals oxides is completely combusted and grinded to a grain size below 2 mm and then the ash is calcined at the temperature of 850°C during 8 hours. 2. The method of use acc. to claim 1 characterised in that the ash from excess sludge is subject to water leaching of alkalis at the boiling point of the water- ash suspension and then to filtering and rinsing with water till obtaining the alkalis content in the product, converted to K2O + Na2O, equal to < 2.5 wt.%. 3. The method of use acc. to claim 1 characterised in that the ash grain size is below 0.5 mm. |
containing transition metals
The subject of the invention consists of the use of ash from the processes of thermal treatment of water or sewage sludge as an oxygen carrier for the fuels combustion or gasification in a process with so-called oxygen looping. In the process of fuels combustion or gasification in a system with oxygen looping, the agents supplying oxygen for the fuel conversion are oxides or their mixtures obtained on the basis of various metals oxides.
The method of sewage sludge use in the form of fertilisers is known from the American application description No US20030121302. The method of use consists in converting a bioorganic material such as e.g. sewage sludge into a wet organically enriched fertiliser mix, enabling obtaining a dried fertiliser in a form of compact pellets. The preparation process enables an effective control of the produced odour and the disinfection of bioorganic material.
The method of sewage sludge drying is known from the description No US 415341 1 . The preparation method consists in drying the sewage sludge using a hot sand and burning a dry sludge.
The method of sewage sludge use as a biofuel is known from the description No US 461571 1 . The invention consists in the use of mixing the sewage sludge with dried foliage to prepare briquettes as a fuel.
The method of briquetting or pelletizing useful for fuels produced based on a substantial amount of sewage sludge combined with a smaller amount of lime as a binder is known from the American patent description No US 5797972. The method of sewage sludge use for fuels production consisting in producing a pumpable slurry of sewage sludge with/or without an addition of carbonaceous fuel and burning this blend in a furnace or boiler is known from the patent description US5264009. The use of sewage sludge for fire extinguishing is known from the description US 20020130294, where the fire suppressant consists of wet cake blocks, used to extinguish fires in buildings and forests.
The sewage sludge use as road and pavement fillers is known, resulting from patent No US 4028130, where it also composes lime, fly ash and possibly alkaline metals sulphates.
Many potential oxygen carriers are known, including various compositions of copper, manganese, iron, cobalt or nickel oxides used as active materials and aluminium oxide, titanium dioxide, zirconium dioxide, sepiolite, bentonite - used as an inert material.
Inert materials are added at the amount from a few to a few dozen wt.% in relation to the active material, due to which the oxygen carriers life is extended, inter alia via the reduction of their attrition.
This invention is aimed at the use of a sewage sludge inorganic fraction as an oxygen carrier in chemical looping.
The method of use of inorganic fractions from the sewage sludge containing transition metals, acc. to the invention is characterised in that pre-dried excess water or sewage sludge containing from 5 wt.% to 95 wt.% of transition metals oxides is completely combusted and grinded to a grain size below 2 mm and then the ash is calcined at the temperature of 850°C during 8 hours.
What is favourable, the ash from excess sludge is subject to water leaching of alkalis at the boiling point of the water-ash suspension and then to filtering and rinsing with water till obtaining the alkalis content in the product, converted to
K 2 O + Na 2 O, equal to < 2.5 wt.%.
What is favourable, the ash grain size is below 0.5 mm.
The method according to the invention has been described in non- restrictive examples of implementation. Example 1
Oxygen carrier sample obtained from a sewage sludge ash. Dried excess sewage sludge containing from 5 wt.% to 95 wt.% of transition metals oxides was subject to complete combustion and grinding to a grain size below 2 mm. The obtained ash was calcined at 850°C during 8 hours.
Detailed analyses of the manufactured product were carried out, including examination of the particle size distribution using a screen and laser analysis, examination of the chemical composition using the X-ray fluorescence {XRF), examination of the ash fusion temperatures and the oxidation and reduction tests using thermogravimetry coupled with a quadrupole mass spectrometer (TG-QMS).
The elemental composition of the ash obtained was as follows (ppm): Fe - 60085, Cu - 854, Zn - 8200, Cr - 321 , Pb - 590, Cd - 10, Mn - 620, Na - 67725, K - 1980, Al - 19268, Ca - 30869.
The oxygen carrier obtained features:
• good oxygen transport capacity at the temperature of 800°C (2.79 wt.%),
• good regeneration ability (Fig. 1 ),
• repeatability of oxidation and reduction results,
• optimal operating temperature range (600 -1200°C),
• high thermal resistance; the melting temperature in a reducing atmosphere amounted to: 1210°C and in an oxidising atmosphere - 1200°C.
• low agglomeration tendency (the grains sticking together was not observed during cyclic oxidation and reduction process),
• small particle size, where 90% of the sample had particles <86.94 μιτι,
• short oxidation and reduction time (-80% of the fraction is reduced within 6.51 minutes and regenerated within 1 .02 minute),
• 100% ability of regeneration, after the hydrogen combustion reaction,
• low production costs and availability due to its origin (waste material).
Time (min)
Fig. 1 - results of cyclic thermogravimetric tests of an ash sample. Example 2
Oxygen carrier sample obtained from a sewage sludge ash subjected to leaching
Dried excess water or sewage sludge containing from 5 wt.% to 95 wt.% of transition metals oxides was subject to complete combustion and grinding to a grain size below 2 mm. The obtained ash was calcined at 850°C during 8 hours. The obtained product was subject to leaching in distilled water. The leaching was carried out during 10 minutes at the boiling point of water-ash suspension containing 20 weight parts of water and 1 weight part of ash. After the solution cooling down, the undissolved part was filtered off and rinsed with fresh distilled water. After the sludge drying it was weighed again and the amount of water- soluble substances was calculated, which for the described example amounted to 3.2%. The leaching was carried out to remove alkaline metal oxides, which presence results in lowering the ash melting temperature. Too low ash melting temperature could make it impossible to use it as an oxygen carrier for fuel thermal conversion in a system with a chemical looping. The removal of alkaline oxides was also aimed at increasing the content of active metal oxides presented in the obtained specimens.
Detailed analyses of manufactured preparations were carried out, including examination of the particle size distribution using a screen and laser analysis, examination of the chemical composition using the X-ray fluorescence {XRF), examination of the ash fusion temperature and the oxidation and reduction tests using thermogravimetry coupled with a quadrupole mass spectrometer (TG-QMS).
The oxygen carrier obtained using the aforementioned method features:
• good oxygen transport capacity at the temperature of 800°C (3.51 wt.%),
• good regeneration capacity (Fig. 2., Fig. 3.),
• repeatability of oxidation and reduction results (Fig. 3),
• optimal operating temperature range (600 - 1200°C),
• high thermal resistance; the melting temperature in a reducing atmosphere amounted to: 1220°C and in an oxidising atmosphere to 1220°C.
• low agglomeration tendency (the grains stucking together was not observed during cyclical process of oxidation and reduction),
• small particle size, where 90% of the sample had particles <89.92 μιτι,
• short oxidation and reduction time (-80% of the fraction is reduced within 6.09 minutes and regenerated within 1 .37 minute),
• 100% regeneration ability, after the hydrogen combustion reaction,
• low production costs and availability due to its origin (waste material).
Time (min)
Fig. 2 - results of cyclic thermogravimetric tests of ash after leaching, 800 ¾- a>
0
300 325 350 375 400
Time (min)
Fig. 3 - repeatability of oxygen transport capacity at the temperature of 800°C of ash after leaching versus time (at transport capacity of 3.5 wt.%).
Example 3
Oxygen carrier sample obtained from the sludge originating from deep waters treatment
Dried excess sludge from deep waters treatment containing from 5 wt.% to 95 wt.% of transition metal oxides was subject to complete burning and grinding to a grain size below 2 mm. The ash obtained was calcined at 850°C during 8 hours.
Detailed analyses of the product manufactured were carried out, including examination of the particle size distribution using a screen and laser analysis, examination of the chemical composition using the X-ray fluorescence {XRF), examination of the ash melting temperature and the oxidation and reduction tests using thermogravimetry coupled with a quadrupole mass spectrometer {TG-QMS).
The oxygen carrier obtained using the aforementioned method features:
• good oxygen transport capacity at the temperature of 800°C (13.86 wt.%),
• good regeneration capacity (Fig. .4),
• repeatability of oxidation and reduction results (Fig. 4),
• optimal operating temperature range (600 - 1200°C), high thermal resistance; the melting temperature in a reducing atmosphere amounted to: 1330°C
low agglomeration tendency (the grains stucking together was not observed during cyclic oxidation and reduction process),
small particle size, where 90% of the sample had particles <58.4 μιτι, short oxidation and reduction time (-80% of the fraction is reduced within
1 1 .9 minutes and regenerated within 2.1 minutes),
100% ability of regeneration, after the hydrogen combustion reaction, low production costs and availability due to its origin (waste material).
Time (min)
Fig. 4 - results of cyclic thermogravimetric tests of a water sludge sample.
The examination results of ash obtained using different methods, without and with leaching, and sludge from the deep water treatment are presented below. Table 1. Oxygen transport capacity versus temperature for two ash samples and for water sludge
Table 2. Time necessary for reduction and regeneration of two ash samples for the preset conversion at the temperature of 800°C
The oxygen transport capacity is defined as the difference between the masses of oxidised and reduced form of the solid oxygen carrier Δ = m ox - m re (wt.%). To determine the oxygen transport capacity of solid oxide carriers obtained in the form of ash and leached ash, originating from the sewage sludge and from the excess water sludge, cyclical examinations were carried out in oxidising (synthetic air) and reducing (3% H 2 /Ar) conditions by means of the coupled TG-QMS technique using a Netzsch STA 409 PC Luxx thermobalance and an Aeolos QMS 403C quadrupole mass spectrometer. In this way the process of chemical looping was simulated in laboratory conditions.
For example, Fig. 1 gives results of cyclical thermogravimetric examinations for a leached ash sample, carried out at temperatures of 600°C, 700°C and 800°C. Table 1 presents the oxygen transport capacity versus oxygen carrier types and temperature. In turn, Table 2 presents the values of time necessary for reduction and regeneration of two ash samples for the following fractional conversions at the temperature of 800°C.