FR2983744A1 - Method for vitrification of ashes produced by gasification process or pyrogasification, involves evacuating flue gases produced by burners during combustion of ashes, and cooling ashes in vitrification chamber - Google Patents

Abstract

The method involves heating of ashes to vitrification temperature by a set of burners using air as oxidant, where the air is enriched with oxygen or purified syngas (6) from a gasification unit (1), or biogas (23), or natural gas (24). The flue gases produced by the burners during combustion of the ashes are evacuated, and the ashes are cooled in a vitrification chamber (26). The ashes are directed towards the gasification unit at one or more points of the gasification unit having a gas treatment unit (14) upstream of the gasification unit.

Description

The present invention relates to a thermal and economical heating mode of an ash vitrification unit and the association thereof with a waste gasification or pyrogasification unit, producing these ashes.

Gasification consists of converting the combustible fraction of the waste consisting of carbon, hydrogen and oxygen into a gas mixture consisting mainly of carbon monoxide CO, hydrogen H 2, methane CH 4, and a large number of volatile compounds of formula CxHyOz, all these bodies being perfectly combustible in the presence of oxygen. Depending on the technology, the gasification can be carried out in a wide temperature range (400 ° C - 1000 ° C). Pyrogasification can be considered as a gasification with a lesser amount of reactive agents, it is generally carried out at low temperature ( below 600 ° C) and produces a gas rich in tars compared to gasification. The gas is commonly called syngas, and also contains water vapor, as well as fine dust, called fly ash. The energy recovery of the syngas can be carried out directly, that is to say without any particular treatment, by combustion in appropriate burners, equipping boilers with production of steam for various uses, process steam and / or turbine for electricity production.

In some cases, it is necessary to purify the syngas, in the case where the energetic valorization is directed towards a combustion in engines with pistons or in gas turbines, these equipments requiring a syngas clean, excluding particularly the presence of dust and acids. The current regulation (European Classification of Waste, transmitted in French law under the decree n ° 2002-540 of April 18, 2002 - rubric 19 - 01 -00) concerning the residues resulting from heat treatment units of waste (incineration, gasification, pyrolysis ) defines ashes as dangerous products because of the contaminants they contain (presence of heavy metals in particular such as chromium, cadmium, mercury, nickel, lead, arsenic ..) which requires expensive specific treatments, carried out at outside the treatment units by specialized companies (inerting by encapsulation then put in special landfills or salt mines) Vitrification allows, by the fusion process implemented, to include the contaminants in a vitreous matrix , thus greatly limiting their danger potential, the ashes in the molten or vitrified state being then considered as waste and inert, and in some cases even exploitable. This operation, as described in the present invention, is carried out in situ, and thus allows the internal control of their treatment, in economic conditions much lower than those requiring the external treatments mentioned above. Ashes originate from the inert or mineral fraction of the waste.

They are produced in the gasification or pyrogasification chain and, except in rare cases, in pulverulent form at several points: under a gasifier (pyrogasifier), under the possible purification of the syngas, under a boiler, under pre-dedusting plant downstream of the boiler.

The proportion of ashes produced under gasifier (pyrogasifier) and those discharged in the raw syngas is variable and depends on gasification techniques. This proportion does not affect the present invention, which can treat them partially or totally, as part of the treatment envisaged.

The final treatment at the end of the gasification unit (pyrogasification), which consists in capturing the residual fly ash and at the same time, neutralizing the contaminations such as acids, volatile heavy metals, organochlorines, and thus produces a powdered residue or under sludge form according to the technology used, is not concerned with the present invention.

The particle size of the ash is variable and ranges from 20 microns to 5 millimeters, depending on the point of collection in the waste treatment chain. Their chemical composition mainly comprises silica SiO 2, alumina oxide Al 2 O 3, lime oxide, CaO, magnesium oxide, MgO, iron oxide Fe 2 O 3, potassium oxide, K 2 O , carbon C, heavy metals (Zn, Pb, Cd, Hg, C, Ni, As). Their melting temperature is generally between 1250 ° C and 1350 ° C. Processes using high-temperature vitrification (greater than 1500 ° C) have emerged using plasma torches, electric arcs, or even in-situ treatment in gasification units using high temperature combustion ( 1400 to 1600 ° C) of all gas from the gasifier (pyrogasifier) to allow a melting of ashes within the gasification unit, this type of solution being called integrated vitrification. It is easy to see that for an integrated vitrification gasification unit, any disturbance (lack of waste fuel supply, gasification control defects or pyrogasification, etc.) can lead to a fall in the temperature of the syngas and thus the risks of taking mass ash molten, a phenomenon that must be avoided at all costs, since it may lead to a prolonged shutdown of the facility. The use of plasma torches or electric arcs requires a high consumption of electricity, and de facto implement temperatures much higher (5000 ° C) than those necessary to obtain the fusion of ashes.

These processes have had virtually no industrial development, given their high operating costs, the need to rely entirely on non-renewable energy, or their unreliability. It seems advisable to use mostly renewable energy released by the combustion of a small fraction of syngas crude or purified (conditioned) representing in energy need 2% to 3.5% of the energy potential entering the gasifier, taken on the main stream from the gasifier / pyrogasifier (raw syngas) or if necessary downstream of the purification (syngaz purified) to ensure the vitrification of the latter in an independent unit, the resulting hot gases being returned to the unit of gasification. This energy requirement corresponds to the energy required to bring the ashes to the vitrification temperature, after deduction of the energy retrocessed by the combustion fumes from the burners of the vitrification chamber, to the gasification unit (pyrogasification).

The variation of 2.5% to 3.5% is related to the ash content of the waste considered and the restitution temperature of the gases, which varies according to the vitrification temperature used. Similarly, it seems advisable to be able to use another source of gas, such as biogas, if the gasification unit is located near a methanisation unit operating on domestic waste, urban sludge, effluents with predominantly organic components even a household waste landfill, if it is equipped with a biogas capture network. Similarly, it seems advisable, to supplement if necessary, with natural gas and in small proportions since the lower heating value of natural gas is 8 to 10 times higher than that of syngas, any significant variation in the quality of syngas, which could result from any significant variation in the quality of the waste or the operation of the gasifier (pyrogasifier), in order to be able to maintain the vitrification temperature constant and thus avoid a build-up by cooling in the vitrification chamber. The use of natural gas can also compensate for a prolonged shutdown of the gasifier (pyrogasifier), allowing in the limit of the ash storage buffer capacity, continue to vitrify them. The syngas burners currently exist, they allow to obtain without problem stable flame temperatures between 1450 ° C and 1550 ° C. In the event of possible temperature insufficiency, these burners may be doped with natural gas or possibly with oxygen-enriched air, in an adjustable proportion depending on the composition of the syngas used. To facilitate the treatment, if it turns out that the ash melting temperature is high (above 1400 ° C), it seems advisable to use fluxes in qualities and proportions that will be defined according to the type of ash used. The ash vitrification chamber, can be designed according to the principle of vitrification furnaces aiming to produce industrial glass (patent publication No. 2,654,021 has fallen into the public domain since December 7, 2009) It is generally in the form a tunnel coated internally with suitable refractories, depending on the product (s) to vitrify. The tunnel is carried and heated to the required temperature by a battery of burners judiciously positioned. The number of syngas burners depends on the size and design of the above-mentioned vitrification chamber, bearing in mind that a syngas burner is generally larger than a conventional burner using natural gas. Feed pipes for raw or optionally purified syngas, whose temperature may vary, according to the gasification (pyrogasification) and / or conditioning processes, from 300 ° C. to 700 ° C., will be insulated or even electrically drawn in the case of use of crude syngaz rich in tars (from 5 to 100 gr / Nm3 syngaz or more) tars generally condensing at temperatures of 300-350 ° C, in order to avoid any condensation of these products in the pipe feed.

Similarly, it seems advisable to return the combustion gases from the burners to the gasification unit (pyrogasification) to recover the energy contained and their treatment (purification) in the main unit. The chamber will therefore comprise a sheath lined internally with refractory discharging combustion gases from the burners, generally at temperatures above 1200 ° C, to the gasification unit (pyrogasification), generally at the inlet of the recovery boiler. These gases are polluted, in particular by volatile heavy metals and certain halogenated fractions rich in chlorine and sulfur contained in the ash from the gasifier 10 (pyrogasifier). They will therefore join the main gas flow in the gasification unit (pyrogasification), and will therefore undergo the appropriate treatment at the same time as the latter. The molten ash, at the outlet of the vitrification chamber, arrives gravitarily to a chamber full of water to be brutally cooled, this resulting in fragmentation into small elements (a few millimeters to a few centimeters). The water vapor produced joins the smoke exhaust duct where it mixes. The ashes, thus recovered in vitreous form, have demonstrated to be of great stability and a very weak potentiality to release by leaching the initial contaminants, thus making them assimilable to inert waste type. 20 Potential recovery routes have been identified (Public Works ..) but remain to be created, depending on potential markets and regulations. The ash vitrification unit from a gasification (pyrogasification) treatment line shown in the following drawing comprises an ash vitrification chamber 26, supplemented with peripheral equipment such as ash storage with device 32. extraction and supply of ash to the vitrification furnace. This vitrification chamber can receive at the same time as the ashes, melts of different chemical composition, via similar systems 21 (Fondant A) and 22 (Fondant B) comprising storage, extraction and supply to the vitrification chamber 26. 30 The vitrification chamber is equipped with several burners 25 specially designed for combustion in air or enriched air, or oxygen, simultaneous or not, of crude syngas 3 or optionally purified 6, biogas 23 and natural gas 24. Downstream, an extraction duct 27 by ventilation, using the depression in the boiler 8, the combustion gases of the aforementioned burners and the water vapor resulting from the sudden cooling of the ashes, with venting 28, and isolation valves, if it is necessary to isolate the vitrification chain from the gasification treatment (pyrogasification). Downstream also, a chamber 30 for brutal cooling of the vitrified ashes using a water inlet 29, from which the vitrified ash is mechanically extracted. 40 The gasifier (pyrogasifier) 1 produces a lean gas, called crude syngaz 2 more or less rich in tars, from the conversion of waste and / or fuels 17, via reagents 18, which can be air air enriched with oxygen, oxygen, water vapor, alone or in mixture.

The mineral fraction, resulting from the inert fraction of waste and not converted into syngas, is generally extracted in the form of powdery ash 19, more or less hot (from 200 ° C to 700 ° C) depending on the agent introduction systems. reagents and the type of gasifier (pyrogasifier).

The raw syngas can be according to the valorization mode of the latter (gas engine, gas turbine), purified by a system 4 for reducing dust or fly ash, as well as contaminants such as hydrochloric acid or sulphide. hydrogen, formed in the gasifier (pyrogasifier). In this case, the fly ash 7 collected at this stage will join the ash storage 32. An energy recovery mode of the widely used raw or purified syngas is represented by a boiler 8, producing water vapor, which is generally superheated ( 360 to 500 ° C) and under relatively high pressure (15 to 90 bar) used either in industrial processes or in turbines for the production of electricity.

The syngas is then burned in specific burners installed on the boiler and converted into fumes. The flue gas paths in the boiler collect, by impact effect, fly ash, which is led by an adequate transport system 10, then 31, to the ash storage 32.

At the outlet of the boiler there is very often a pre-dewaterer 11, which collect upstream of the flue gas treatment, fly ash, brought by a suitable system 13, then 31, to the storage of the ashes 32. The final smoke treatment 14 which receives the fumes 12 from the pre-dust collector (cyclone, or electroflitre, or bag filter) very strongly reduces the dust but also the acids, heavy metals, products of treatment residues which are collected separately by an adequate system 16. These ashes, rich in salts, excess reagents, heavy metals, are not concerned by the present invention. The clean fumes go to the atmosphere via a chimney. 30

Claims (2)

CLAIMS1. Process for the vitrification of ashes from a gasification or pyrogasification process, characterized in that the invention consists in carrying out: The heating up to the vitrification temperature of the ashes by a set of specific burners using as combustionant air, oxygen-enriched air, oxygen and as fuels, either crude syngas 3, optionally purified syngas 5, recovered on the gasification unit (pyrogasification), or biogas 23 from an anaerobic digestion unit or an organic waste storage facility with controlled production of biogas, either natural gas 24, or a mixture in all proportions of these gases. The evacuation of the combustion fumes 27 produced by the above-mentioned burners and the water vapor produced during the abrupt cooling of the ashes coming from the vitrification chamber of the ashes 26 and directed towards the gasification unit (pyrogasification ) producing these ashes, at one or more points of this unit, but in any case upstream of the treatment of fumes 14 of this unit. 2. Process according to claim 1, which consists in collecting all or part of the ashes under gasifier or pyrogasifier 1, under the possible purification of crude syngas 5, under boiler 8, under pre-dedusting device 11, for storage and subsequent supply, by adequate systems 19, 7, 10, 13 and 31 to the buffer storage unit 32, to be vitrified in the chamber 26, with the possible use of flux found in the systems 21 and 22.