Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23L—SUPPLYING AIR OR NON-COMBUSTIBLE LIQUIDS OR GASES TO COMBUSTION APPARATUS IN GENERAL ; VALVES OR DAMPERS SPECIALLY ADAPTED FOR CONTROLLING AIR SUPPLY OR DRAUGHT IN COMBUSTION APPARATUS; INDUCING DRAUGHT IN COMBUSTION APPARATUS; TOPS FOR CHIMNEYS OR VENTILATING SHAFTS; TERMINALS FOR FLUES
  • F23L7/00—Supplying non-combustible liquids or gases, other than air, to the fire, e.g. oxygen, steam
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
  • F23C2900/00—Special features of, or arrangements for combustion apparatus using fluid fuels or solid fuels suspended in air; Combustion processes therefor
  • F23C2900/99001—Cold flame combustion or flameless oxidation processes
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E20/00—Combustion technologies with mitigation potential
  • Y02E20/12—Heat utilisation in combustion or incineration of waste
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E20/00—Combustion technologies with mitigation potential
  • Y02E20/34—Indirect CO2mitigation, i.e. by acting on non CO2directly related matters of the process, e.g. pre-heating or heat recovery

Definitions

• the primary thrust in the development of flame technology has constantly been directed towards the development of fluid dynamic conditions capable of promoting intimate and rapid mixing of fuels with the oxidant. More specifically, reference should now be made to jet flames, in which the energy of the jet is modified with the most various geometries and measures to promote mixing, to promote internal mixing with combusted gases, and forming a positionally stable flame of the desired size.
• the physical place of the flames commonly coincides with the reaction zone in which solid particles are present, or are generated, such particles being the only ones capable of emitting radiation into the visible range, within the temperature range 1000-2500 K. Even flames of gaseous fuels, e.g. methane, emit in the visible range due to the formation of solid carbonaceous nanoparticles (soot, widely proven). Furthermore, for what concerns emissions impacting the environment, flames are associated with the formation of NO x , which rises exponentially with temperature, and of CO due to incomplete combustion.
• the flame is an intrinsically highly complex phenomenon which can be described quantitatively at the macro scale and punctually only at the final front where the reactions in play have already run to completion.
• the phenomenon is essentially chaotic. Any description which may be made is based solely on methods of a statistical nature. Adjacent to ultra-high temperature elementary domains, in which the reactions are already complete, there are cold domains in which the reactions have not yet begun. The heat of reaction is high, but has high threshold values (autoignition above 1100 K) , and steep concentration and temperature gradients are established.
• the flameless condition occurs in the combustion of gaseous fuels, and within ranges of existence defined by dilutions of no less than a ratio of approx. 3 (or a maximum oxygen concentration of approx. 3.5% in the diluted oxidant) and with preheating to no less than the autoignition temperature.
• H2O principally H2O, strong IR absorbers/emitters
• VSA vacuum swing absorption
• the volatile liquid fuels are fed mixed even roughly with water and/or steam
• the nonvolatile liquid fuels high molecular weight organic compounds, i.e. molten organic solids
• the solid fuels are ground to dimensions of a few millimetres, and suspended in water (water slurry) , and fed as a slurry, combustion flue gases are obtained which also have a very low content of NO x and of CO.
• thermodynamic power generation cycles which are simple, highly efficient and have low environmental impact, and, above all, which can process problematic fuels (low ranking fuels) .
• reaction system thus becomes readily controllable both in terms of punctual and average conditions within values which provide access to a novel operating zone where it is possible to achieve more favourable compromises from the standpoint of efficiency and emission reduction for the generation of energy from low ranking fuels.
• the very strong IR radiation (of the order of a
• the combustor of the invention which operates in flameless conditions without preheating of the feeds and without restrictions for maintaining flame stability, materialises the use of low ranking fuels to produce fumes which are at elevated temperature and are substantially free of hydrogenated organic compounds and particulates and yields substantially smaller quantities of gaseous pollutants.
• the availability of the combustor makes it possible to devise high efficiency thermodynamic cycles for the generation of electrical power which cannot otherwise be achieved at a similar level of simplicity.
• One of the preferred embodiments of the present invention is a combustion process for gaseous fuels (H2, CH4, light hydrocarbons, S, syngas and other gaseous fuels with low caloric value) in a high temperature refractory-lined reactor, with the aim of generating power.
• the reactor operates with fuel(s) and oxidant premixed with steam, and/or combustion flue gases, introduced into the two streams using various known methods.
• the two streams are fed separately, the fuel preferably being fed to the axis of the reactor, and the oxidant at a plurality of peripheral points around the fuel.
• high power IR radiation instantaneously preheats the reactants on input, said reactants being intrinsically transparent to IR ( 2, O2) but rendered opaque and thus IR absorbers thanks to dilution with steam.
• a particularly uniform and controlled reaction front (flameless, mild combustion, volume combustion) develops until both the fuel and the oxidant are completely consumed.
• the reaction proceeds without there apparently being a lower limit for preheating of the fed reactants.
• it is preferable for the concentration of the opaque gases in the feeds not to fall below 30%.
• combustion reaction carried out according to the criteria of the process makes it possible to achieve negligible emissions of soot, TOC, CO, NO x even when operating with oxidant (oxygen, air) at a ratio 1.05 close to stoichiometric conditions, i.e. with excesses very much lower than the ratio 2 essential in the prior art.
• the overall process for energy generation consists ( Figure 2) , for example, in drawing in air (1) and compressing it in the axial compressor (CI) to pressures of between 1600 and 2500 kPa abs .
• Compression may be adiabatic according to the prior art; isothermal compression is preferred, with direct injection of deionised water into each stage of the compressor, or by means of intermediate tapping of gas into which water is injected up to saturation and subsequent reintroduction into the compressor.
• the compressed gas is sent (4) to the heat recovery unit (E) .
• the recovery unit uses the exhaust gases (8) output from the turbine (T) at a temperature of approx. 800-900 K. It is more preferred ( Figure 2) to use the heat recovery unit (E) as a saturator, according to the prior art, by introducing preheated water (3) at a plurality of points during the course of oxidant preheating.
• the gaseous fuel (2) is compressed in the compressor (C2) in accordance with the isotherm concept by means of injection of water.
• the compressed oxidant and fuels preheated to 600 K and preferably to 700 K, the difference between the two cases being accounted for by a greater and a lesser quantity of water vaporised and added (between 40 and 60% by weight relative to the sum of fuel plus oxidant, and until recovery of all the heat contained in the gases discharged by the turbine) , are sent (5 and 6) to the combustor (R) .
• Complete combustion is performed in the reactor and the outlet gases reach a temperature of 1400 K and preferably higher temperatures of up to 1600 K, corresponding to the upper operating temperature limit for prior art turbines with cooled ceramic blades.
• the gases from the combustor are sent (7) to the turbine (T) for isoentropic expansion to atmospheric pressure and a temperature of around 700-800 K, variable as a function of steam content.
• the outlet flue gases from low-grade heat recovery (E) are sent (9) to the condensing steam recovery section (B) .
• the condensing section may comprise finned tube heat exchangers or condensing columns with recirculation of cooling water in towers, or combinations of both types.
• system of the invention is exceptionally flexible with regard to acceptable fuels, including low-grade fuel gases and fuel gases obtained from systems for gasifying low-grade solid fuels, for example biomass and refuse. Further flexibility of the system of the invention is manifested in its management and efficiency when the required electrical load is varied.
• the combustor of the invention provides stable combustion over a wide load range (from 20% to 120%) with very low load losses (on the contrary, jet flames predominantly consume and are efficient over a much tighter range of operability) - adjusts the delivered power by adjusting the addition of steam, at a constant fume temperature, so adjusting the flow rate and molecular weight at the turbine being appropriately refractory-lined, the combustor may be kept hot in stand-by status with a pilot flame, and with a fuel consumption of less than 1% of the rated load, ready to be started up to maximum power within a very short time .
• the minimum thermodynamic efficiency of the (electrical/thermal) cycle in the above-stated configurations of the invention is 50% and rises to values of around 60% in the event of heat recovery by saturator and a reaction at 1600 K. This is thanks to the power required to compress the oxidant having been halved, to the fact that the addition of water only has an impact on the cycle in terms of pumping energy and to the recovery of low-grade heat from the spent flue gases down to 350 K.
• This energy efficiency is accompanied by scarcely noticeable emissions at the combustor outlet, namely TOC of the order of ppm, CO always below 10 ppm, NO x of the order of a few tens of ppm and only at higher combustion temperatures.
• 90% oxygen is used as oxidant, the oxygen being produced from air by means of a prior art enrichment process involving selective adsorption on zeolites.
• the enrichment section supplies 90% oxygen at atmospheric pressure with overall specific consumption of electrical energy of around 0.1 kWh/kg of O2.
• the oxygen may be used to enrich the combustion air (injected into the axial compressor at the position corresponding to 250 kPa) or to replace the air entirely.
• Another preferred embodiment of the process is a process for combusting liquid fuels (hydrocarbons, heavy refinery fractions, bitumens, spent solvents, orimulsion, liquid fuels having a variable content of solid breakdown products, water and sulfur) in a high temperature refractory-lined reactor, with the aim of generating energy.
• liquid fuels hydrocarbons, heavy refinery fractions, bitumens, spent solvents, orimulsion, liquid fuels having a variable content of solid breakdown products, water and sulfur
• the reactor operates with fuel(s) premixed with water, and with oxidant premixed with steam introduced into the streams using various known methods.
• the two streams are fed separately, the fuel preferably being fed to the axis of the reactor, and the oxidant at a plurality of peripheral points around the fuel.
• reaction front flameless, mild combustion
• the reaction proceeds without there being any apparent lower preheating limit. However, it is preferable for the concentration of the opaque gases in the feeds not to fall below 30%.
• the problems of scaling up the reactor are similar to those already examined for the gas combustor and may be solved with the design shown in the attachment.
• the reactor is characterised by TOC, CO, NO x and carbonaceous particle emissions which are barely noticeable and considerably below the prior art, though operated with a fuel/oxidant ratio approaching 1.
• the overall process for the generation of power may be that already introduced for gaseous fuels, with the exception of inevitable adjustments required by good engineering practice to take account of the different nature of the fuel (liquid) .
• the overall process may be of the structure shown in the diagram below ( Figure 3) .
• the air oxidant (1) is compressed in the compressor (C) up to the pressure of 350 kPag.
• the compressed oxidant is sent (4) to the heat recovery unit (E) which on the air side effects progressive saturation with steam, utilizing the low-grade heat output (10) by the steam recovery and production boiler (S2) , and preheating to 400- 500 K.
• the level of preheating and the content of added steam are, however, such as to ensure complete utilisation of the low-grade heat to temperatures of 350 K.
• the liquid fuel (2) is mixed with water (3) , and preheated with low-grade heat .
• Oxidant and fuel (5 and 6) are sent to the combustor (R) , for complete combustion, at fume temperatures of 1600 K, preferably 1900 K if the fuel contains ash to be coalesced in the reactor in the molten state.
• the hot gases are sent (7) to the radiant zone of the supercritical steam production boiler (SI) .
• the outlet gases at a temperature of 1100 K and a pressure of 350 kPa absolute, are sent (8) to the turbine (T) for expansion to atmospheric pressure. They are then sent (9) to the downstream heat recovery sections (S2) for the production of steam, most often existing plant, up to a temperature of 600-700 K.
• the steam produced by the boiler is sent to the expansion turbine for energy generation, according to known methods.
• the process of the invention permits: emissions of TOC, particulates, CO, NO x which are reduced to a particularly low, virtually insignificant, level substantially reduced corrosion and erosion in boilers due to the absence of particulates and uncombusted organic compounds, so permitting higher temperatures while using identical materials design of the radiant part of the boiler of small dimensions efficiency of the electrical/thermal power generation cycle of greater than 50%.
• One possible variant of the cycle comprises the addition of a section for the production of 90% oxygen by means of the prior art process involving selective adsorption on zeolites. The section provides oxygen at atmospheric pressure, and may partially or completely replace compressed air. Overall efficiency falls, but not significantly.
• Oxygen is preferable in particular when fuels with a high sulfur content are used, because it enables efficient and compact chemical post-treatment of the fumes for desulfurisation prior to discharge into the atmosphere. Using oxygen also makes it feasible to complete the water cycle with a positive balance by using a final condensation section which is small in size and low in cost.
• Another preferred embodiment of the process is a combustion process for solid fuels (pit coal, high-sulfur coal, lignite, animal flours, refuse in granular form) in a high temperature refractory-lined reactor, with the aim of generating power.
• the reactor operates with fuel ground to less than a mm in size and carried with water.
• the oxidant is premixed with steam introduced into the stream using various known methods.
• the two streams are fed separately, the fuel preferably being fed to the axis of the reactor, and the oxidant at a plurality of peripheral points around the fuel.
• the principle of operation is similar to that described above for the gaseous fuel combustor and the liquid fuel combustor.
• Emissions can be observed in the visible range, as with traditional flames, but the range of emissions, with particular reference to CO and NO x , is more then an order of magnitude lower than that known in the prior art for the combustion of coal.
• a particularly uniform and controlled reaction front develops until both the fuel and the oxidant are completely consumed.
• the reaction proceeds without there being any apparent lower preheating limit. However, it is preferable for the concentration of the opaque gases in the feeds not to fall below 30% by weight.
• the ash melts, in some cases with the assistance of a moderate addition of flux (sodium and potassium carbonate, Si ⁇ 2), and, when fused, readily coalesces and is collected at the bottom of the combustor, in accordance with the recent teaching of PTO Itea.
• flux sodium and potassium carbonate, Si ⁇ 2
• the reactor is characterised by TOC, CO, NO x and carbonaceous particle emissions which are barely noticeable and considerably below the prior art, though operated with a fuel/oxidant ratio approaching 1.
• the overall process for the generation of energy may be that already stated for gaseous fuels, with the exception of inevitable adjustments required by good engineering practice to take account of the different nature of the fuel (solid) . It may also be that already stated for liquid fuels, always taking account of adjustments dictated by good engineering practice.
• the above-stated variants also apply to solid fuels.
• the process of the invention makes it possible: also to utilise highly efficient, high temperature (>900 K) supercritical steam boilers with low quality coal (ash content, sulfur) ; something which has been completely impossible in the prior art due to the "slagging" problems caused by fused ash on the tubes, which is highly corrosive at elevated temperature to operate, using identical materials, supercritical plant at still higher temperatures due to the total absence of hydrogenated organic compounds .
• Overall electrical energy/thermal energy efficiency is greater than 50%.
• a further still more preferred embodiment of the process of the present invention which may be derived in accordance with good engineering practice in order to make full use of the features of the combustor of the invention, is represented by the process for combusting low-grade, gaseous, liquid and solid fuels of the previous embodiments, and preferably solid fuels, with 90% oxygen as oxidant, in the combustor of the invention inserted in a thermodynamic cycle directed towards maximising yields (diagram attachment 3) .
• the combustor operates at a pressure of 1600-2500 kPa.
• the solid fuel (0) is fed to the reactor in the form of a slurry in water.
• the 90% oxygen (obtained by VSA) (1) is saturated with water and compressed in an axial compressor (Cl) equipped with multiple injection points for preheated water (2) from the final fume heat recovery unit (R2) .
• the compressed oxidant is sent to the combustor, mixed with steam (3) obtained from the recovery unit R2 operating on the outlet gases from turbine (Tl) , and with combusted gases (4) compressed by means of the compressor (C2) coupled to the expansion turbine Tl.
• the combustor operates at temperatures of above 1700 K. Incombustible fractions are reduced to vitrified slag (5) .
• the outlet flue gases from the combustor (6) are mixed with gases compressed by the compressor C2, so dropping in temperature to 1150-1200 K, and sent to the expansion turbine Tl.
• the expanded gases at atmospheric pressure (7) pass through the recovery units Rl, undergo dry deacidification in tower DA, and continue onward in the recovery section in recovery unit R2.
• the cold gases, at 370 K and close to the dew point, are in part returned (8) to the intake of compressor C2 and compressed to 1600-2500 kPa, using a similar method to that of compressor Cl, i.e. with injection of preheated water (9) in R2 which maintains the temperature throughout compression and at the outlet close to the saturation T (470-490 K at the outlet) .
• Thermodynamic efficiency of the cycle is greater than 60%.
• the proposed process is a more advanced and distinctly higher performance alternative even in comparison with complex and sophisticated prior art IGCC (Integrated Gasification Combined Cycles) .
• An externally cooled metal structure, a reactor lined with refractory material and with an internal volume of 5.3 m ⁇ is taken into consideration.
• the reactor is fed with light fuel (or methane) and air with the aim of gradually raising (100 K/hour) the surface of the reactor to a temperature of above 1200 K.
• the reactor On completion of the pre-heating phase, the reactor is fed with recycled flue gases, cooled to 550 K, and oxygen (oxygen content 87-93%, originating from the VSA unit) premixed with flue gases before entering the reactor, and it is pressurised.
• oxygen oxygen content 87-93%, originating from the VSA unit
• the surface temperature of the walls is monitored by pyrometers. Quartz portholes, at both ends, provide an internal view.
• the temperature of the outlet gases from the reactor is monitored, both by a laser diode sensor, which detects H2O absorption/emission, and by a high-temperature Zr thermocouple.
• the flue gases from the reactor are detected by a set of fast response analysis units (T95: 1.5 seconds), specifically developed by Fisher-Rosemount, capable of monitoring both the bulk compounds, H2O, CO2, and the "micro" compounds, CO, NO, O2, SO2 and TOC (Total Organic Content, hydrogen CO2 flame detector) .
• the analytical units analyse the gases at a frequency of 10 hertz.
• the original signal is recorded, skipping the data smoothing software.
• the closed cycle flue gases of the reactor are monitored in parallel, as soon as they are laminated to atmospheric pressure, by a group of FTIR sensors which detect H 0, C0 2 , SO2, CO, N2O, NO, NO2, HC1 with a response time of 40 seconds.
• the preheated reactor of Example 1 is fed with light fuel and maintained at a pressure slightly above atmospheric. Over an 8 hour cycle, the fuel feed rate is gradually increased, from 1.5 litres/minute to 4 litres/minute, in order to increase the temperature of the flue gases from 1500 K to 2100 K with a gradient of 60-80 K/hour.
• Oxygen is fed to the reactor at a constant ratio to fuel, in such a manner as to maintain the excess of oxygen in the flue gases between 4 and 1.8 mol% .
• Recycled fumes are adjusted to allow an increase in the temperature of the flue gases.
• Example 3 (as Example 2, but at a pressure of 400 kPa absolute)
• Example 4 (as Example 1, but at a pressure of 700 kPa absolute)
• the flame zone is very limited at the beginning and rapidly disappears .
• the above-described reactor is fed with air and light oil (23
• a wide flame zone is always present, from the feed zone (inverted cone) approx. to the centre of the reactor.
• NO ranges from 250 ppm up to more than 1000 ppm (although the absolute reading may be questionable since it is four times the scale of the analytical sensor) .
• TOC starts from above 50 ppm and never falls below 20 ppm. CO is always within the 30- 70 ppm range.
• Example 1 The reactor of Example 1 is fed with heavy oil, HHV 41500 kJ/kg, comprising 17% by weight asphaltene, 8% carbonaceous material, with 90% content oxygen and recycled flue gases cooled to 550 K.
• the operating pressure is maintained at 400 kPa absolute.
• the heavy oil is preheated to 450 K in the feed lines, and injected into the reactor through a steam actuated sprayer.
• the fuel feed rate is held constant at 5 litres/minute, while the feed rate of the recycled flue gases is controlled in such a manner as to reproduce the temperature gradient of
• Example 7 (as Example 6, but a heavy fuel feed rate of 10 litres/minute) .
• the temperature of the cool flue gases is 580 K.
• Example 8 (as Example 6, but at a pressure of 700 kPa absolute)
• Example ⁇ The same sequence as in Example ⁇ was performed, but the oxygen feed rate is increased so as to obtain an excess of
• Example 6 A white zone of visible flame which is much wider (relative to Example 6) located close to the feed port was observed through the quartz porthole. The flame zone shrank progressively, but remained wider than that in Example 6. ODC reveals a qualitative change corresponding to these observations and to the change in wavelength.
• Example 6 A sequence comparable with that of Example 6 was performed with oxygen directly fed into the reactor, in a position which is assumed to initiate internal mixing with the flue gases, but remote from the axial feed port.
• Orimulsion (70% aqueous emulsion) is fed at 6 litres/minute through a steam actuated sprayer with an 8 mm orifice.
• South African coal caloric value 28500 kJ/kg, 17% by weight ash and 9% moisture content, is screened in such a manner as to obtain an average particle diameter of 2 mm (maximum particle size 4 mm) .
• Olive husk originally coarsely ground into particles of an approximate diameter of 1-2 mm, caloric value 18400 kJ/kg, 8% by weight incombustible ash and 11% moisture, 0.7 organic nitrogen, is suspended in water (ratio: 1 kg of olive skin per 0.8 kg of water) in a stirred tank to obtain a pasty but still pliable liquid mix.
• the liquid mix is pumped to the reactor of Example 1 and injected with a steam propelled sprayer through a 12 mm orifice.
• 90% title oxygen is premixed with recycled cold flue gases and is fed to the reactor in a proportion such as to maintain a level of 4 to 8% oxygen in the resultant flue gases.
• the reactor loop is at an absolute pressure of 400 kPa.
• the feed rate of the liquid mix is held constant, by means of the volumetric pump, at around 1 rtvVh (more precisely, 8 hours' operation totalized 9.65 ⁇ of slurry), while the recycled cool flue gases are controlled in such a manner as to reproduce the gradient of the fume temperature slope of Examples 2-4 and 6-11, over the range 1900-2100, before then holding the fume temperature level at 2100.
• higher T values are required in order to melt incombustibles (e.g. alkaline earth and metal oxides) .
• Fused slag is drained from the lower part of the reactor, is cooled and carried away by a pressurised water loop.
• the characteristics of the vitrified slag are stated in the following list:
• Iso-kinetic sampling of the fly ash is set up at the reactor outlet.
• the solids are trapped on a 0.7 micron PTFE membrane filter.
• the sampling line and filter box are electrically heated and thermally insulated in order to avoid condensatio .
• One 8 hour sample and some shorter duration samples were taken. 8 hour average 18 mg /Nm 3 low temperature phase of 1/2 hour 3 ⁇ m g/N m 3 (3 samples) 1/2 hour at elevated temperature ⁇ 5 (4 samples, all close to the lower limit of the technique)
• Example 12 (Comparison Example, with reference to Example 11)
• the reactor of Example 1 is preheated to a wall temperature, in the vicinity of the outlet port, of 1600 K, and fed with air and pulverized (mean 20 microns) coal at 800 kg/hour.
• a venturi diffuser is fitted to the air feed tube just before the feed port.
• the pulverised coal is fed through a slot located in the narrow section of the venturi, and suspended in air in an air/coal ratio of 14.0 Nm ⁇ /kg.
• Cryogenic oxygen is added to the air to maintain the desired gradient of the temperature curve, namely 4-8% excess oxygen in the flue gases.
• the run is interrupted after 4-6 hours due to the apparent degradation of boiler performance in relation to the flue gases, given an increase in cooled fumes temperature from 530 to 590 K, by the way a temperature which is close to the operating temperature limit of some devices installed on the cold fume side. Later on, the inspection of the fumes-in-the- pipe boiler reveals considerable fouling of the pipes caused by the ash, and ash build-up in dead spots.
• the analytical value always exceeds 1500 ppm (more precise figures are meaningless, being more than six times greater than the analyser scale) .
• Example 1 The reactor of Example 1 is fitted with double propulsion chambers, fast cycle (0.2 hertz) fed with compressed air at 11 bar to feed granular solids to the pressurised reactor.
• the dry 1:1 mixture of screened coal and olive waste from Example 11 is fed to the propulsion chambers in small quantities, pressurised and injected discontinuously.
• the feed rate of the mixture is held constant at approximately 800 kg/hour over the 8 hours of the sequence.
• the 90% oxygen is premixed with recycled cold fumes, and fed to the reactor in a proportion such as to maintain the excess of oxygen in the flue gases produced at between 4 and 8%.
• the reactor gas loop is pressurized at a pressure of 400 kPa absolute.
• the recycled fumes are adjusted so as to reproduce the reactor fumes temperature slope of the experimental runs

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