Patent Description:
A pulse combustion dryer, or pulse combustion spray dryer, is a kind of dryer that atomizes liquids or pasty products inside a drying chamber. To generate the spray, a pulse combustion burner is used.

A pulse combustion burner, has a cylindrical combustion chamber where fuel (usually a gaseous fuel like natural gas, propane, LPG etc., or a liquid fuel), is injected in a continuous way. On the other hand, air is introduced in a pulsating way, that means, air is introduced through a valve that opens and closes between <NUM> and <NUM> times per second, or at higher frequencies. That makes the combustion to be a pulsating or oscillating combustion, at same frequencies. The outlet of the combustion chamber is a narrow tailpipe. Combustion gases, combustion heat, and a number of pulses of between <NUM> and <NUM> times per second or more, leave the combustion chamber through the tailpipe. When the frequency of the pulses is more or less equal to the natural resonance of the combustion chamber and/or the tailpipe, the combustion reaches resonance and the pulses get a higher amplitude or pressure oscillation. Pulse combustion burners are widely described in prior art. In some configurations, pulse combustion burners work valveless, and the pulsating of the combustion can suck the air without the need of valves. Known fuels used in pulse combustion dryers are fuel gases such as natural gas, methane or hydrogen, and liquid fuels such as alcohol.

The end of the tailpipe is connected to a drying chamber, in this point a liquid or pasty product is introduced through a suitable injector. The pulses or strong pressure oscillations break the liquid or paste into thousands of small droplets, and the stream of hot combustion gases accelerate those droplets to near the speed of sound, which dramatically increases the heat and mass transfer rates. As a result, a spray is generated inside the drying chamber that evaporates the water from the droplets in an extremely short time, without product overheating, transforming the liquid or pasty product to be dried, into a dried powder.

Dried powder, combustion gases and evaporated moisture, leave the drying chamber to a powder separation system, which normally is a cyclone and/or a bag filter. In the end, an aspiration fan sucks the gases and directs them to a stack.

<CIT> discloses a pulse combustion dryer for dewatering a fibrous web in paper manufacturing using an unspecified fuel.

<CIT> discloses a pulse combustion dryer which may use hydrogen as a fuel in which the burner is designed to generate a pulsating flame for generating a pulsating hot gas flow as a swirl burner having a diffuser as element at is outlet.

<CIT> discloses a pulse combustion dryer which may use hydrogen as a fuel wherein an externally drivable pulsation device for at least a part of the mass flow directed to the burner is arranged upstream in the pipeline leading to the flame.

<CIT> discloses a pulse combustion dryer which may use hydrogen as a fuel which comprises a processing engine for generating a high velocity airstream and directing the high velocity airstream into an acceleration tube, the high velocity airstream having sufficient volume, heat and velocity to vaporize substantially all water present in an organic material stream; a work chamber mounted to the acceleration tube of the processing engine, the high velocity airstream routed into the work chamber, and the work chamber terminated within a micronizing dryer; and an injector pump to inject the organic material into the work chamber for interaction with the high velocity airstream.

<CIT> discloses a pulse combustion dryer which may use hydrogen as a fuel, comprising a line located upstream the flame connected to an independent, externally driven pulsation device for at least a part of the mass flow directed to the burner.

One problem of operating the burner of a pulse combustion dryer with hydrogen and oxygen in stoichiometric conditions, is that the combustion temperature will be higher than <NUM>. Such a high combustion temperature can melt or highly damage the burner. The solution given to that problem according to prior art is basically to circulate cooling water inside the walls of the pulse combustion burner, by means of, e.g., a cooling jacket or cooling coil, which makes the burner complex to build, and makes the operation of the pulse combustion dryer risky in case of cooling water failure during operation.

A first aspect of the invention relates to a pulse combustion dryer wherein hydrogen is used as a fuel and wherein exhaust gases from the pulse combustion dryer are used efficiently to regulate the temperature in the pulse combustion burner.

A second aspect of the invention relates to a pulse combustion dryer using hydrogen as a fuel, which does not require circulating cooling water inside the walls to lower the combustion temperature below <NUM>.

A third aspect of the invention relates to a pulse combustion dryer that allows recirculating a portion of the water steam that leaves the dryer, into the combustion chamber of the pulse combustion burner for cooling the pulse combustion burner.

According to the invention, there is provided a pulse combustion dryer comprising.

The flow rate and the speed at which the water steam is deviated towards and introduced into the pulse combustion chamber may depend on different factors such as the temperature difference between the inside of the pulse combustion chamber and the water steam, the volume of the pulse combustion chamber and how much the temperature of hot combustion gas passing to the dryer chamber is to be reduced, among others.

In some embodiments, the product feeding line may comprise a free end with an injector arranged within or at the end of the tailpipe to inject the product to be dried into the drying chamber.

In some embodiments, the pulse combustion dryer may further comprise at least one steam blower arranged in the steam supply line for sucking water steam from the steam outlet line.

In some embodiments, the steam supply line comprises:.

In some embodiments, the oxygen inlet is arranged in the first branch downstream the first steam blower.

In some embodiments, the pulse combustion dryer may further comprise an aspiration fan arranged in the steam outlet line in a position between the steam supply line and the connection of the outlet line to the powder separation system for keeping a vacuum pressure of <NUM> to <NUM> mbar below atmospheric pressure in the drying chamber.

In some embodiments, a valve, for example a rotary valve, may be arranged in the steam supply line upstream the at least one steam inlet of the pulse combustion burner. The valve is configured to operate such that it is able to provide a pulsed water steam flow entering the pulse combustion chamber.

In some embodiments, the separation system comprises a cyclone connected to an outlet of the drying chamber and to the steam outlet line.

In other embodiments, the separation system comprises a bag filter connected to an outlet (9a) of the drying chamber and to the steam outlet line.

In still other embodiments, the separation system comprises a cyclone connected to an outlet of the drying chamber, and a bag filter connected to the cyclone and to the steam outlet line.

In further embodiments, the separation system comprises a cyclone connectable to an outlet of the drying chamber and to the steam outlet line, and a bag filter connectable to the cyclone and to the outlet of the drying chamber, and connected to the steam outlet line.

In some embodiments, the steam outlet line can contain a filter, like an activated carbon filter or similar, to eliminate organic volatile compounds than can volatilize from the dried product during the drying process. These organic volatile compounds are eliminated, in particular, from the water steam once separated from the dried product.

The pulse combustion dryer according to the invention provides some advantages, e.g.:.

Other aspects, advantages and features of the invention become apparent from the present specification and drawings.

To complete the description and in order to provide for a better understanding of the invention, a drawing is provided. Said drawing forms an integral part of the description and illustrates an embodiment of the invention, which should not be interpreted as restricting the scope of the invention, but just as an example of how the invention can be carried out. The drawing comprises the following figure:
<FIG> shows a schematic view of an embodiment of a pulse combustion dryer according to the invention.

The reference signs in this drawing have the following meanings:.

In the embodiment shown in <FIG>, the pulse combustion dryer comprises a product tank <NUM> for containing a liquid or a pasty product to be dried, an injector <NUM>, a pulse combustion burner <NUM>, a drying chamber <NUM>, a cyclone <NUM>, and a bag filter <NUM>.

The tank <NUM> is connected to a tailpipe 4a of the pulse combustion burner <NUM> by a product feeding line 1a to the injector <NUM> which is arranged at end of the tailpipe 4a. The tailpipe 4a connects an outlet of the pulse combustion burner <NUM> to an inlet of the drying chamber <NUM>. The pulse combustion burner <NUM> comprises a combustion chamber 4b and a hydrogen inlet connected to a hydrogen gas train <NUM>. A feeding pump <NUM> is arranged in the product feeding line 1a.

The drying chamber <NUM> comprises an outlet 9a which is connected by an outlet line 9b to an inlet of the cyclone <NUM>, and also to a first bypass line 9c which is connected to an inlet of the bag filter <NUM>. A first check valve <NUM> is positioned in the first bypass line 9c to open or close access to the first bypass line 9c and a second check valve 15a is positioned in the outlet line 9b between the inlet of the cyclone <NUM> and the connection of the outlet line 9a and the first bypass line 9c, to open or close the outlet line 9a. In the embodiment shown, the cyclone <NUM> and the bag filter <NUM> constitute a particle separation system. In other embodiments, the particle separation system comprises only the cyclone <NUM> or only the bag filter <NUM>.

The cyclone <NUM> comprises an outlet which is connected to an inlet of the bag filter <NUM> through an outlet line 10a, and to a second bypass line 10c connected to the steam outlet line 13a. The bag filter <NUM> comprises a steam evacuation outlet 11a which is also connected to the steam outlet line 13a. A third check valve <NUM> is connected in the outlet line 10a to open or close access to the outlet line 10a, and a fourth check valve 15a is positioned in the second bypass line 10c to open or close access to the second bypass line 10c.

A steam supply line <NUM>,14a,14b derives from the steam outlet line 13a, downstream the steam evacuation outlet 11a of the bag filter <NUM> and the connection of the second bypass line 10c to the steam outlet line 13a. An aspiration fan <NUM> is arranged in the steam outlet line 13a in a position between the steam supply line <NUM>, and the steam evacuation outlet 11a of the bag filter <NUM> and the connection of the second bypass line 10c to the steam outlet line 13a.

The steam supply line <NUM> comprises a first branch 14a and a second branch 14b which are each connected to a respective steam inlet of the pulse combustion burner <NUM>. A first steam blower <NUM> is arranged in the first branch 14a and an oxygen gas train <NUM> is connected to the first between the first steam blower <NUM> and the corresponding steam inlet of the pulse combustion burner <NUM>. A second steam blower <NUM> is arranged in the second branch 14a of the steam supply line <NUM>.

In operation, the liquid or pasty product to be dried, is pumped by pump <NUM> through the product feeding line 1a, from product tank <NUM> to the injector <NUM> that within the tailpipe 4a of the pulse combustion burner <NUM>.

The pulse combustion burner <NUM>, uses hydrogen H<NUM> as fuel and oxygen O<NUM> as an oxidizing agent for the combustion. Hydrogen flow can come from an in-situ electrolysis process, or can be any other conventional hydrogen source. The hydrogen is introduced in the pulse combustion burner <NUM> through a proper hydrogen gas train <NUM>, in a constant mass flow.

Instead of using a blower to introduce combustion air into the pulse combustion burner <NUM>, like conventional pulse combustion burners do, according to this invention, a first steam blower <NUM> introduces water steam into the pulse combustion burner <NUM>. Preferably, the water steam is introduced through a valve, e.g., a rotary valve, (not shown in <FIG>), because this allows controlling the frequency of pulsations, independently from other combustion parameters like combustion temperature. When a valveless pulse combustion burner <NUM> is used, the water steam will enter the pulse combustion burner <NUM> without the need of valves or a blower, using the aspiration provided by the pulses of the pulse combustion burner <NUM> itself.

The steam blower <NUM> sucks a portion of the water steam flowing through the steam outlet line 13a, into the steam supply line <NUM> which means that a portion of the water steam is recirculated after the product has been dried, and there is no need of a specific water steam generator or an external water steam supply.

Pure oxygen O<NUM> provided by the oxygen gas train <NUM> is introduced into the first branch 14a of the steam supply line <NUM>, as the oxidizing agent for combustion in the combustion chamber 4b of the pulse combustion burner <NUM>. This oxygen supplied may originate from an in-situ electrolysis process, from an air purification process, or can come from any other conventional oxygen source. The oxygen is introduced through a proper oxygen gas train <NUM>, in a constant mass flow.

Hydrogen mass flow is constant and is directly proportional to the amount of water that has to be evaporated from the liquid or pasty product to be dried. Oxygen mass flow is also constant and stoichiometric to the hydrogen flow combustion. Water steam flow from the first steam blower <NUM>, is controlled by the desired combustion temperature in the pulse combustion burner <NUM>, i.e., when a lower combustion temperature is desired, a higher flow of water steam is blown, and vice versa. Without this adjustable water steam flow, combustion temperature would be higher than <NUM>, but using the adjustable water steam flow, temperature can be cooled down to <NUM> to <NUM>. No cooling jacket or coil is needed to protect the pulse combustion burner <NUM> from overheating.

In this way, pure water steam is the only product of the combustion in the combustion chamber 4b of the pulse combustion burner <NUM>. Additionally, the second steam blower <NUM> (optional) in the second branch 14b can be used to get cooler temperatures around the product injector <NUM>, and to direct spray to the inside the drying chamber <NUM>.

Water steam leaves the pulse combustion burner <NUM> at a temperature between <NUM> and <NUM>, which means that superheated water steam is the drying medium in all the volume of the drying chamber <NUM>. Water steam from the pulse combustion burner <NUM>, together with the pulses generated, hit the liquid or pasty product to be dried that is introduced through the injector <NUM>. Atomization of the product takes place in drying chamber <NUM>, and water from droplets is quickly evaporated, so that the water steam in the drying chamber <NUM> is cooled down from between <NUM>-<NUM>, to a lower temperature between <NUM> and <NUM>, depending on the product to be dried. Temperature at which the mixture of powder and water steam leave the drying chamber <NUM>, is controlled by the flow of product to be dried; if a lower temperature is desired, flow is increased, and vice versa.

To avoid condensation, any point of the drying process between product injector <NUM> and the steam outlet <NUM>, have to be at least <NUM>, at atmospheric pressure. At pressures lower than atmospheric, less than <NUM> can be reached without steam condensations in the pulse combustion dryer.

After leaving the drying chamber <NUM> through the outlet 9a thereof, the mixture of gases, i.e., water steam from pulse combustion burner <NUM> and evaporated moisture from the product to be dried, and powder, are led through the outlet line 9b to the cyclone <NUM>, or through the first bypass line 9c directly to the bag filter <NUM> through the first bypass line 9c.

The steam/product mixture exiting the drying chamber <NUM> may be guided through the outlet line 9a only the cyclone <NUM> and from there through the second bypass line 10c, so that water steam coming from the cyclone <NUM> is guided to the steam outlet line 13a by closing outlet line 10a by means of the third check valve <NUM> and opening the second bypass line 10c by means of the fourth check valve 16a. Alternatively, the steam/product mixture exiting the drying chamber <NUM> may be guided through the outlet line 9a and the first bypass line 9c only to the bag filter <NUM>, so that water steam coming from the bag filter <NUM> is guided to the steam outlet line 13a, by opening the first check valve <NUM> and closing the second check valve 15a. In another alternative, the steam/product mixture exiting the drying chamber <NUM> is guided to the cyclone <NUM> through the outlet line 9b by closing the first check valve <NUM> and opening the second check valve 15a, and from the cyclone <NUM> to the bag filter <NUM> through the outlet line 10a by opening the third check valve <NUM> and closing the fourth check valve 16a, so that water steam coming from the bag filter <NUM> is guided to the steam outlet line 13a. Election of the path of the flow of the steam/product mixture exiting the drying chamber <NUM> only through the cyclone <NUM> or only through the bag filter <NUM> or both the cyclone <NUM> and the bag filter <NUM> depends on the properties of the product to be dried. The cyclone <NUM> and the bag filter <NUM> are provided respective powder outlets 10b, 11b allowing extraction of the dried powder product which has been separated from the water steam.

The aspiration fan <NUM> sucks the water steam originating in the drying chamber <NUM> which is present in the cyclone <NUM> and/or the bag filter <NUM>, to keep a slight vacuum pressure of <NUM> to <NUM> mbar below atmospheric pressure in the drying chamber. A higher vacuum can be used, if low drying temperatures are desired without water steam condensation problems. A portion of the water steam sucked by the fan <NUM> through the steam outlet line 13a, is sucked into the steam supply line <NUM> and blown towards through the first branch 14a by action of the first steam blower <NUM> and, where desired, also to through the second branch 14b by action of the second steam blower <NUM>, to the respective steam inlets of the pulse combustion burner <NUM>. Thereby, a portion of the water steam coming from the drying chamber <NUM> and from which the dried product has been removed, is recirculated by the first steam blower <NUM> and, optionally, by the second steam blower <NUM>, into the pulse combustion burner <NUM>, whilst the remaining water steam leaves the pulse combustion dryer through the steam outlet <NUM>.

The gas flow in the outlet line 13a is a pure, or almost pure water steam flow. The amount of water steam leaving the pulse combustion dryer <NUM> through steam outlet <NUM>, basically equals the amount of water evaporated from the product to be dried, plus the water steam generated in hydrogen and oxygen combustion. This makes the pulse combustion dryer work as a superheated water steam dryer.

As apparent, the pulse combustion dryer of the invention provides some advantages, e.g.:.

In this text, the terms first, second, third, etc. have been used herein to describe devices, elements or parameters. It will be understood that the devices, elements or parameters should not be limited by these terms since the terms are only used to distinguish one device, element or parameter from another. For example, the first branch could as well be named second branch, and the second branch could be named first branch without departing from the scope of this disclosure.

Claim 1:
A pulse combustion dryer comprising
a pulse combustion burner (<NUM>) having a cylindrical pulse combustion chamber (4b), to generate a pulsating combustion, a drying chamber (<NUM>) and a tailpipe (4a) connected to the pulse combustion chamber (4b) for receiving and pressurizing pulses of hot combustion gas, and to the drying chamber (<NUM>) for receiving pressurized pulses of hot combustion gas,
a hydrogen inlet for feeding hydrogen into the pulse combustion chamber (4b),
a product feeding line (1a) for feeding a liquid or pasty product to be dried into the drying chamber (<NUM>) to produce a spray of water steam and dried product powder,
a powder separation system (<NUM>, <NUM>) having at least one powder outlet (10b, 11b) connected to the drying chamber (<NUM>) to separate the dried product powder and water steam coming from the drying chamber (<NUM>),
a steam outlet line (13a) connected to the powder separation system (<NUM>, <NUM>) to evacuate water steam,
characterized in that the pulse combustion dryer further comprises an oxygen inlet for feeding oxygen into the pulse combustion chamber (4b)) and in that
the steam outlet line (13a) is connected to a steam supply line (<NUM>, 14a, 14b) which is connected to at least one steam inlet of the pulse combustion burner (<NUM>), the steam supply line (<NUM>, 14a, 14b) for deviating at least a portion of the water steam that passes through the steam outlet line (13a) to the at least one steam inlet of the pulse combustion burner (<NUM>) to enter the pulse combustion chamber (4b) as a cooling medium at a rate of water steam sufficient for cooling the hot combustion gas passing to the dryer chamber (<NUM>) to a reduced gas temperature of between <NUM> to <NUM>; and
the oxygen inlet is arranged in a portion of the steam supply line (<NUM>, 14a, 14b) to mix oxygen and water steam that passes through the steam supply line (<NUM>, 14a, 14b) to the at least one steam inlet of the pulse combustion burner (<NUM>).