Patent Publication Number: US-2012040295-A1

Title: Method and an apparatus for producing carbon dioxide and thermal energy

Description:
TECHNICAL BACKGROUND 
     The invention relates to an apparatus for producing very pure carbon dioxide containing gas and thermal energy. The invention also relates to a method for producing carbon dioxide containing gas and thermal energy, as well as the use of such an apparatus and a method. 
     Carbon dioxide can be used for a number of purposes. It can be directly applied in various uses, and on the other hand, it is suitable as a raw material for many processes. However, carbon dioxide is a problematic product, because emissions of it contribute to the greenhouse effect. Therefore, the controlled production of carbon dioxide is of primary importance. 
     In atmospheric air, the content of CO 2  is about 380 ppm. When plants are grown in a greenhouse, the content of CO 2  will drop to a level of about 150 to 220 ppm if no supplementary CO 2  is added. At a level of about 800 ppm, the growth of, for example, cucumber, tomato and lettuces, as well as tulips, has been found to increase by about 30 to 50% in a greenhouse. 
     On the other hand, impurities in carbon dioxide containing gas slow down the growth of plants. For example, nitrogen oxides at a level of 0.1 to 2 ppm block the fertilizing effect of supplementary CO 2 . Also, for sulphur oxides, the highest allowed levels range from 0.015 to 0.1 ppm, depending on the duration of exposure. For ethene (C 2 H 4 ), the allowable limits are even more stringent, from 0.002 to 0.01 ppm. The strictest limits are for hydrogen sulphide, which is only allowed at a level of 0.001 ppm. 
     Thermal energy, and partly also carbon dioxide, is conventionally produced by burning to be used in, for example, greenhouses. The fuels suitable for this burning must be pure. The combustion takes place at a high temperature, and oxides of nitrogen and sulphur are easily formed as side products, and some of the ethene remains unburnt. The strict standards for purity of CO 2  hinder the application of gas produced in thermal combustion in greenhouses. Special Low NOx or Ultra Low NOx burners are needed to reach the level of 50 to 80 ppm in the production of nitrogen oxides. Even when strongly diluted, they do not meet the latest requirements set for plants. 
     Furthermore, the production of pure carbon dioxide containing gas is relatively expensive and involves relatively complex technology. In small greenhouses, pure carbon dioxide is used in the form of bottled gas or liquid. Used in this way, the costs of carbon dioxide become very high. The costs of the gas for a greenhouse may be almost in the order of the heating costs. 
     DESCRIPTION OF THE INVENTION 
     Now, an apparatus has been invented for producing thermal energy and/or very pure carbon dioxide (CO 2 ) containing gas, which is technically very simple and has particularly low emissions of impurities. 
     To achieve this aim, the invention is characterized by the features which will be presented in the independent claims. The other claims will present some advantageous embodiments of the invention. 
     The apparatus according to the invention, which is suitable for producing thermal energy and very pure carbon dioxide (CO 2 ) containing gas, comprises at least one injector for injecting fuel and at least one main blower for supplying combustion air, and the production apparatus comprises at least one catalytic combustion unit with at least one catalytic burner for catalytic combustion of fuel effectively at a temperature of 350 to 850° C. in a retention time of 0.01 to 0.1 s, and at least one heat exchanger for at least partial transfer of heat from the gas produced in combustion to the combustion air and fuel to be supplied to the catalytic burner, and the production apparatus comprises at least one catalytic afterburner for at least partial after purification of the gas produced in combustion. 
     Said at least one catalytic afterburner connected to the burning unit guarantees and improves the purification results of the catalytic burner further. It enables different ways of running, and even in connection with reversals, the gas can be guided through a burner. 
     According to one aspect of the invention, the production apparatus comprises at least one gas recirculating device for guiding the gas formed in combustion at least partly to the main blower. This solution improves substantially the energy balance of the plant, because the need to heat combustion air is reduced; advantageously, the content of recirculated gas is greater than 50%, such as 70 to 90%. 
     According to one aspect of the invention, the catalytic production apparatus comprises gas guiding members for guiding the flow of gas from the first stage of the catalytic burner to a catalytic afterburner and/or to another stage of the catalytic burner. This will make the usability of the plant even more versatile. 
     According to one aspect of the invention, the heat exchanger is selected from a group consisting of a two-stage heat exchanger, a multi-stage heat exchanger, and a rotary-bed heat exchanger. These are technologically and economically advantageous solutions. Preferably, the heat exchanger is regenerative. 
     According to one aspect of the invention, the catalytic combustion unit comprises a two-stage or multi-stage heat exchanger and gas distribution means for guiding the flow of gas during a change in the direction of gas supply. This solution, too, makes the use of the apparatus more versatile and is technically and economically advantageous. 
     According to one aspect of the invention, in the gas formed in the combustion (CO2G), the level of nitrogen oxides (NO x ) is lower than 5 ppm and the level of ethene (C 2 H 4 ) is lower than 1 ppm, calculated for an oxygen content of 3 vol %. According to one aspect of the invention, in the gas formed in the combustion (CO2G), the level of nitrogen oxides (NO x ) is lower than 2 ppm, calculated for an oxygen content of 3 vol %. These levels are implemented by controlling the combustion conditions of the production apparatus so that these low contents are achieved. 
     The formed carbon dioxide containing gas CO2G typically contains about 14 to 17 wt % of carbon dioxide, such as 15 wt %, when for example fuel oil or gases are applied. In the apparatus according to the invention, the level of nitrogen oxides is advantageously lower than 5 ppm, calculated for an oxygen content of 3 vol %. For example, in a gas diluted for use in a greenhouse, the level of nitrogen oxides is thus advantageously lower than 0.1 ppm. According to one aspect of the invention, the level of nitrogen oxides in the afterpurified carbon dioxide containing gas is lower than 2 ppm, calculated for an oxygen content of 3 vol %. Such a gas can be used particularly well in, for example, a greenhouse. 
     In the apparatus according to the invention, a gaseous or liquid fuel can be burnt catalytically in a controlled manner by means of a catalyzer at a low temperature, 350 to 850° C., so that very little nitrogen oxides (NO x ) and sulphur oxides (SO X ) are produced by combustion, and as a result of almost complete combustion, negligible levels of hydrocarbons and carbon monoxide are left in the gas. The level of ethene, which is the most harmful of hydrocarbons to plants, is lower than 1 ppm, calculated for an oxygen content of 3 vol %. In diluted fertilizer gas, the content is less than 0.01 ppm, as well as the content of carbon monoxide. The thermal energy produced in combustion can be advantageously used for heating, and the cooled pure combustion gas can be led to utilization. The untreated exhaust gases of the heating boiler according to the invention are so pure that they meet even the most stringent international standards for emissions. 
     The content of other emissions, such as sulphur oxides, will depend on the sulphur content of the fuel. To keep the sulphur emissions low as well, low emission fuels should be used, such as propanol, natural gas, bioalcohol, light fuel oil, pyrolysis gases, or the like. The plant will then clearly meet all the standards for emissions. (NOx and CO&lt;100 mg/Nm 3 ) 
     Preferably, catalytic combustion takes place at a low fuel content below 20% from the LEL limit, which means a content of about 10 g/Nm 3 . This is to prevent the temperatures from rising too high at the oxidation stage. The flow of gas discharged from the boiler is kept low by recirculation. The temperature of the gas is about 50 to 90° C., depending on the heat exchange rs. Even from that, energy can still be recovered by means of a separate heat exchanger. 
     Because there is no separate purification of flue gases in the catalytic combustion plant, energy can be efficiently recovered from the flue gases directly in the actual useful heat exchanger, which may take place by the countercurrent principle. 
     In catalytic combustion according to the invention, the temperature is 350 to 850° C. The catalyzer lowers the combustion temperature by about 100 to 400° C. compared to thermal combustion which typically requires a temperature of 750 to 950° C. This temperature difference is very significant, because at the lower temperature, the nitrogen present in the air does not start to react with the oxygen in the air, and harmful nitrogen oxides are thereby not developed. The catalytic combustion is very fast, having typically a duration of only 0.01 to 0.1 s, such as about 0.02 to 0.05 s, in the catalyzer itself and after that, for example, about 0.1 s in the channel before the heat exchanger. This duration is about one tenth compared with the duration in a thermal boiler. Because the applications according to the invention apply a relatively low temperature and a very short retention time, hardly any nitrogen oxides (NOx) can be formed, their level remaining preferably below 5 mg/Nm 3 . Furthermore, in catalytic combustion, the oxidation is controlled so closely that hydrocarbons and eventual carbon monoxide burn out, their levels being normally lower than 5 mg/Nm 3 . 
     The investment costs of a catalytic boiler are lower than those of thermal boilers with their purification systems. The operating costs of thermal combustion are increased by the costs of acquisition, use and maintenance of a reducer. 
     In thermal combustion, nitrogen oxides are usually formed at such a high level that they must be removed in large boilers. The removal takes place in a selective catalytic reducer (SCR) in which the reducing agent used is ammonia or urea dissolving into ammonia and carbon monoxide gas. The reduction takes place in a special catalyzer so that one molecule of ammonia reduces one NOx molecule. Urea or ammonia is normally needed in about 3 to 4% of the fuel content, and it is even more expensive than the fuel. In other words, it raises the combustion costs respectively. Because the SCR catalyzer will require a temperature of about 230 to 300° C. to operate well, yet another heat exchanger must be provided after the catalyzer. 
     Because the SCR catalyzer requires a long retention time of about 0.3 s (space velocity of 10 to 12,000 1/h), its size is very large. It is often larger in size than the boiler. Furthermore, the SCR will require a tank of ammonia or urea and an automatic dosing system. Both ammonia and urea are difficult substances in their own way. Ammonia is very toxic to transport and store. The urea solutions used are almost saturated aqueous solutions with a solid content of 32 to 40%. They are easily crystallized and difficult to dose. Moreover, both urea and ammonia reduction will require an oxidation catalyst to eliminate possible leaks of ammonia. 
     In the apparatus according to the invention, no additional energy will be needed for continuous operation. Only during startup, the catalyzer/thermal burner and the heat exchanger must be heated to the operating temperature, and thus the operating costs of the plant are very low. 
     According to one aspect of the invention, the injector comprises means for at least partial combustion of the fuel supplied. In the beginning, the incoming gas is heated, if necessary, to the combustion temperature, and after that, part of the energy produced in catalytic combustion can be transferred to heat the incoming gas. 
     According to one aspect of the invention, the apparatus is formed of two parts: the catalytic combustion plant and the heat exchanger. The catalytic combustion plant may be either a regenerative or a recuperative apparatus. In it, the incoming liquid fuel is first vaporized, and the gas is then heated in the heat exchanger, after which it is oxidized in the catalyzer. Part of the produced energy is transferred to heat the incoming gas, and part is led via a post-catalyzer to the heat exchanger for useful energy. After this, the gas flow that had heated the incoming gas and the gas flow passed via the recovery of useful energy are combined. The main part, preferably 70 to 90%, of this gas flow is recirculated to the inlet side of the catalyzer, and the rest of the gas is discharged via a flue gas duct to atmospheric air. 10 to 30% of clean air which contains the oxygen needed for catalytic combustion is admixed to the gas flow entering the catalytic combustion. In many cases, the most advantageous efficiency is achieved when air is only admixed in the required amount, about 10%. 
     In some applications, the heat exchanger may be made of a fire-resistant material. This improves the strength of the plant and increases reliability and reduces the need for maintenance. 
     According to one aspect of the invention, the apparatus comprises an after heat exchanger for recovering heat from gas formed in the combustion and/or for aftercooling the carbon dioxide containing gas discharged from the combustion unit. After the catalytic combustion, an essential part of the heat can thus be recovered via the heat exchanger for the purposes of heating a greenhouse, and the clean CO 2  containing flue gas can be led, for example, into greenhouses for the purposes of fertilizing and partly heating. 
     According to one aspect of the invention, the after heat exchanger comprises means for producing hot water and/or district heat. This will improve the total economy of the production apparatus further. 
     According to one aspect of the invention, the production apparatus is used particularly for producing both thermal energy and carbon dioxide (CO 2 ) containing gas that is very pure in terms of nitrogen oxides, ethene (C 2 H 4 ) and hydrogen sulphide. According to one aspect of the invention, the production apparatus is used particularly for producing thermal energy. According to one aspect of the invention, the production apparatus (PA) is used particularly for producing carbon dioxide (CO 2 ) containing gas that is very pure in terms of nitrogen oxides, ethene (C 2 H 4 ) and hydrogen sulphide. The selected object of production will affect the temperature to be used in combustion. For the production of heat, temperatures from 600 to 800° C. are preferably used, and for the production of carbon dioxide (CO 2 ) containing gas, the temperatures of catalytic combustion may range, for example, from 350 to 500° C. or from 500 to 700° C., depending on the quantity of the gas to be produced and on the object to be filled in. 
     According to an aspect of the invention, the fuel is selected from the group of butane, propane, natural gas, fuel oil, biogas, bioalcohols, organic solvents, pyrolysis gases, and light fuel oil. The utilization of such fuels is technologically advantageous and simple. By using the catalyzer, it is possible to oxidize various gaseous and liquid fuels which may be fossil or various biofuels from renewable sources (alcohols, gases released by pyrolysis, biogas, etc.). It is also possible to oxidize catalytically emissions of volatile organic solvents (VOC) or carbon monoxide either as such or in combination with other actual fuels. 
     According to one aspect of the invention, the apparatus comprises means for diluting carbon monoxide containing gas and leading it to a greenhouse. In this embodiment, the production apparatus according to the invention has technical and economical advantages. Preferably, the thermal energy produced by combustion can be used entirely for heating when the cooled pure combustion gas can be led into a greenhouse for fertilization with CO 2 . The thermal energy remaining in the cooled combustion gas also contributes to the heating of the greenhouse. It is advantageous, for example, when the greenhouse is used in the winter. 
     The gas combustion unit may be a metal honeycomb system with a rotary structure, comprising a catalyzer and a heat exchanger unit one after the other. The gas comes in from one side first into the heat exchanger, in which the gas is heated, and it then enters the catalyzer, in which the gases are oxidized. Next, the gas passes through the other side which collects heat. The structure may also be a honeycomb system in two parts, wherein one cell is used for collecting heat and the other is used for heating incoming gas. 
     According to one aspect of the invention, the catalytic burner comprises two or more stages. This arrangement makes the apparatus controllable in a more versatile way and contributes to the efficiency of the combustion. 
     The heat exchanger may be advantageously coated with a catalytically active coating. This will further improve the efficiency of the production apparatus. 
     The heat exchanger may also be a honeycombed system with a steel structure and consisting of two parts, wherein one cell is used for collecting heat and the other is used for heating incoming gas. The direction of flow is reversed after the cell that heats the incoming gas has cooled to a given limit value. The other cell that has trapped heat from the exhaust gas will start to heat the incoming air. 
     By optimizing the internal flow and dimensioning the heat exchanger formed by thin sheets, the ratio of energy entering the greenhouse via the fertilizing gas and the heat exchanger can be easily controlled. 
     According to one aspect of the invention, the production apparatus comprises one or more heat exchanger and/or catalyzer means which are advantageously made of thin corrugated metal sheets, with channels between them for conducting gas. This kind of a structure is used as a static mixer. The structure increases substantially, for example, the number of contacts of hydrocarbons with a catalytically active surface. This so-called Sherwood number (Sh), representing the efficiency of mass transport, increases from 2.5 to 12; in other words, the gas molecules to be burnt are almost five times more frequently in contact with the catalytically active surface. With the intensified contact, the fuel can be made to burn completely (SAE 2002-01-0357). 
     The heat exchanger can be made of a steel sheet having a thickness of 0.2 to 1.5 mm and being coated with Al and/or Zn or being acid-proof, by corrugated “strips” with a width of 100 to 200 mm, in the same way as the catalyzer. This kind of a mixing structure will substantially intensify the transfer of heat from the gas into the steel sheet, and vice versa. The Nusselt number, representing the heat transfer in a flow channel, will increase from 2.5 to 12, compared with a straight channel. This will improve substantially the efficiency of the heat exchanger. 
     The heat exchanger is advantageously a metal honeycomb system with a rotary structure, which is passed through by gas that is heated in the catalyzer to the required combustion temperature, which is typically 500 to 700° C. The heat exchanger may be made of, for example, creased (corrugated) metal band or wire mesh. 
     The catalyzer may be a rotary metal honeycomb with a shape similar to that of the heat exchanger. The gas comes in from one half, through both/all of the cells. In the accumulator cell, the gas is heated to the combustion temperature, and in the catalyzer following the accumulator, the gases are oxidized. After that, the gases enter the other half of the heat exchanger, in which most of the heat is transferred to the accumulator cell. The rotation speed of the accumulators is preferably 0.3 to 5 rpm. 
     The combustion apparatus according to the invention comprises no bulky tube systems or valves. It is very advantageous in its structure, wherein the acquisition and operating costs are very low compared with the prior art. Also, the operation and maintenance of the apparatus is very inexpensive. Furthermore, the process is simple and efficient to control. 
     According to one aspect of the invention, the production apparatus comprises at least two processing compartments placed within each other. In this embodiment, the catalyzer and the heat accumulator do not rotate but the gas flow direction is reversed at intervals by valves or by temperature control. They are advantageously connected to each other by one or more connecting parts to introduce the gas to be processed into the processing compartments within each other, and the gas purification production apparatus also comprises one or more adjustable gas guiding parts for discharging gas and/or for supplying it into the processing compartments within each other. By means of the connecting parts, it is advantageously possible, for example, to reverse the gas flow direction in the processing compartment. Thus, the same connecting part can be used both for supplying and for discharging gas, depending on the flow direction. In this way, the apparatus can be made not only technically but also economically advantageous. 
     Preferably, the processing compartments within each other have a cylindrical shape. Preferably, there is a cylinder inside and an annular cylinder outside. These are made preferably by winding corrugated bands first around a central axis. After all the foil layers have been wound in the central part, its exterior is lined with sheet iron, outside which an annular part of equal volume is wound and is provided with an outer lining, and flow control valves are fixed to the lower part. 
     The processing compartments can be preferably provided in a common body which is also equipped with the gas flow channels that replace a tube system. By building the channels as part of the structure, an advantageous integrated configuration is achieved. With these solutions, a compact size and simple structural approaches are achieved which clearly reduce the costs compared with the prior art. Thanks to the space saving achieved with the compact structure and the removal of an external pipe system, it is not possible to install a combustion plant of even 8 MW in a 6 m container. 
     The operation of this so-called two-bed combustion plant requires the reversal of the flow direction at intervals of about 30 to 200 seconds. In a conventional two-bed plant, a small quantity of unpurified gas is discharged into atmospheric air when the direction is reversed. In the plant according to the invention, this problem is advantageously solved with the valve arrangement shown in the chart. A valve in a by-pass channel on top of the furnace is opened at the same time when the main channel is closed. After this, the flow direction is reversed by control valves. 
     During the time of the reversal of the flow direction, the gas is passed via catalyzers directly into the by-pass channel. After this, the by-pass channel is closed and the main channel is opened. During the reversal of the direction (3 to 5 s), no energy is accumulated in the heat exchanger by which the incoming gas is heated. 
     According to one aspect of the invention, the production apparatus applies catalyzers made of noble metal and having a very large surface area, which are known for their resistance to so-called catalyzer toxins and high temperatures. With such catalyzers it is possible to achieve an efficiency of even more than 99.9% in the long term. The predicted lifetime of such a catalyzer may be as long as 20 years. 
     According to one aspect of the invention, the production apparatus comprises one or more particle filters. The filter secures the undisturbed operation of the plant and advantageously reduces the particle emissions of the plant. 
     The production apparatus according to the invention can be made relatively compact, because the functions are integrated with respect to each other in its structure. The volume/capacity ratio of such a plant is good, and furthermore, the volume can be used efficiently. This will facilitate transportations and installations on the site of use. The container does not require a foundation or any supporting structures. The production apparatus can be coupled to be ready for use very fast, for example in a couple of days. The container can be advantageously moved to a new location, if necessary. For example, a combustion plant with a capacity of even 3 MW can be advantageously installed in a standard marine container (6 m). 
     Preferably, the production apparatus is automated. It can automatically adjust its operation for various loads, and its operation can be controlled either by a computer or by a GMS phone, if desired. 
    
    
     
       SPECIFIC DESCRIPTION OF THE INVENTION 
       In the following, some embodiments of the invention will be described in detail with reference to the appended drawings. 
         FIG. 1  shows a schematic chart on a production apparatus with a rotary bed heat exchanger. 
         FIG. 2  shows a schematic chart on a production apparatus with a two-stage heat exchanger. 
         FIG. 3  shows a schematic chart on a production apparatus with a two-stage thermal boiler as an after heat exchanger. 
     
    
    
       FIG. 1  shows a production apparatus PA comprising one main blower  1  of combustion air AIR, equipped with an injector J for injecting fuel PG into the combustion air AIR, as well as a catalytic combustion unit  2 . Confined in the combustion unit  2 , substantially inside its walls  2 W, there is a catalytic burner NCB for catalytic burning of fuel at a temperature of 350 to 850° C. in a retention time of 0.01 to 0.1 s for generating carbon dioxide containing gas. In front of the main blower, there is a particle filter PF which improves the operation of the plant and reduces the particle emissions of the plant in an advantageous way. The injector J comprises means for at least partial burning of the fuel PG to be supplied. The production apparatus comprises a rotary-bed RHE regenerative heat exchanger for transferring heat from the carbon dioxide containing gas CO2G generated in the catalytic burner to the combustion air AIR to be supplied into the catalytic burner NCB, and to the fuel PG. The catalytic combustion unit  2  is equipped with a catalytic after burner ACB for after purification of the carbon dioxide containing gas CO2G. The production apparatus PA also comprises an after heat exchanger AHE for aftercooling the carbon dioxide containing gas CO2G discharged from the combustion unit  2 . 
       FIG. 2  shows a production apparatus PA comprising one main blower  1  of combustion air AIR, equipped with an injector J for injecting fuel PG into the combustion air AIR, as well as a catalytic combustion unit  2 . Confined in the combustion unit  2 , substantially inside its walls  2 W, there is a catalytic burner NCB for catalytic burning of fuel at a temperature of 350 to 850° C. in a retention time of 0.01 to 0.1 s for generating carbon dioxide containing gas. In front of the main blower, a particle filter PF is provided to improve the operation of the plant and to reduce the particle emissions of the plant in an advantageous way. The injector J comprises means for at least partial burning of the fuel PG to be supplied. The production apparatus comprises a two-stage regenerative heat exchanger THE for transferring heat from the carbon dioxide containing gas CO2G generated in the catalytic burner to the combustion air AIR to be supplied into the catalytic burner NCB, and to the fuel PG. The catalytic combustion unit  2  is equipped with a catalytic after burner ACB for after purification of the carbon dioxide containing gas CO2G. Above/after the furnace there is a by-pass channel with a by-pass valve BBV which is opened at the same time when the main valve MV in the main channel is closed. After this, the flow direction is reversed by the control valves of the two-stage heat exchanger (not shown in the figures). During the time of the reversal of the flow direction, the gas is passed via catalyzers directly into the by-pass channel. After this, the by-pass channel BBV is closed and the main valve MV is opened. During the reversal of the direction, which takes about 3 to 5 s, no energy is accumulated in the two-part heat exchanger by which the incoming gas is heated. The production apparatus PA also comprises an after heat exchanger AHE for aftercooling the carbon dioxide containing gas CO2G discharged from the combustion unit  2 . 
       FIG. 3  shows a production apparatus PA comprising one main blower  1  of combustion air AIR and an injector J for injecting combustion air AIR and fuel PG, as well as a catalytic combustion unit  2 . Confined in the combustion unit  2 , substantially inside its walls  2 W, there is a catalytic burner NCB for catalytic burning of fuel at a temperature of 350 to 850° C., such as advantageously at a temperature of 600 to 800° C., in a retention time of 0.01 to 0.1 s for generating carbon dioxide containing gas. In front of the main blower, a particle filter PF is provided to improve the operation of the plant and to reduce the particle emissions of the plant in an advantageous way. The production apparatus comprises a two-stage regenerative heat exchanger THE for transferring heat from the carbon dioxide containing gas CO2G generated in the catalytic burner to the combustion air AIR and the fuel PG to be supplied into the catalytic burner NCB. The catalytic combustion unit  2  is equipped via a main valve MV with a catalytic after burner ACB for after purification of the carbon dioxide containing gas CO2G. Part of the gas is guided after the catalytic combustion into the by-pass channel BBV via the heat exchanger THE, to maintain the process heat. Furthermore, the production apparatus PA is equipped with an after heat exchanger AHE for recovering heat from the gas CO2G formed in the combustion. Moreover, the production apparatus PA is also equipped with a gas recirculation apparatus CG for returning the gas CO2G formed in the combustion at least partly to the main blower  1 ; preferably, the content of recirculated gas is 70 to 90% of the discharged gas.