Abstract:
An auxiliary power unit (APU), a method of operating an APU and a vehicle comprising the APU are provided. The APU includes a fuel processor and a fuel cell, the fuel processor being provided with steam, air and dimethyl ether (DME). In order to avoid decreased functionality of the fuel cell caused by lubricants in the DME, a heat exchanger is provided for separating lubricant from the DME.

Description:
BACKGROUND AND SUMMARY 
     The present invention relates to an auxiliary power unit (APU), methods of operating an APU and a vehicle comprising said APU and/or said method. 
     One way to provide electric power and heat to the truck driver&#39;s welfare when not driving the truck is to use the engine as a power source. This is often an inefficient way to produce electricity and heat both from fuel consumption and emission aspects, and will also be subject to legal restrictions in the near future. Typical engine effiencieny at idle is around 5-10%. One way which this is solved is with an auxiliary power unit (APU) consisting of a fuel processor for converting diesel to hydrogen and a fuel cell for converting hydrogen to water and electric power. 
     To lower the demand for oil, there are ongoing work for alternative fuels. One alternative fuel is dimethyl ether (DME). For these vehicles there will also be a need for an APU. A fuel processor for DME may be simpler in construction than a diesel fuel processor with lower working temperature and fewer gas cleaning steps. In EP01060535B1 a fuel cell able to be used with DME as feed is described. With this fuel cell the APU can be simplified to just a fuel cell, water recovery, cooling and fuel and air pumping to the fuel cell. 
     However, a problem with DME is its very low lubricating properties. Therefore there is a need to mix DME with a small amount of lubricant before sold as fuel. This lubricant may have very different properties for fuel processing and may eventually cause the DME fuel processor to make gases not suited for a fuel cell. Another problem with APU&#39;s is the need of water to the fuel processor and the fuel cell, this is solved by condensing water from the fuel cells off-gases see e.g., U.S. Pat. No. 7,036,466B2. The cooling for the water condensing could be arranged by blowing ambient air by a fan. However this cost energy for the fan and can also be inefficient and even impossible in some climate due to the low condensing temperature needed. Some solutions of the latter is described in U.S. Pat. No. 6,759,154 and DE10337607. 
     As explained above, there is a problem associated with DME mixed with lubricant for the functionality and/or properties for the fuel cell in an APU. 
     It is desirable to provide an APU in which the above mentioned problem with DME mixed with lubricants is at least reduced or eliminated. 
     In a first example embodiment an auxiliary power unit (APU) comprising a fuel processor and a fuel cell, said fuel processor is provided with steam, air and DME. Said APU further comprising an afterburner for combusting rest fuel from the fuel cell, wherein exhaust gases from said afterburner is used for heating a first heat exchanger. Said fuel processor is preparing the vehicle fuel to a fuel suitable for the fuel cell and said fuel processor is provided between said fuel reservoir and said fuel cell. The interpretation of preparing is meant to include for instance one or more of the following: transformations, distillations, any form of reactions, adsorptions, absorptions, change of state of aggregation, mixtures, solutions, etc. 
     In another example embodiment said first heat exchanger has at least one inlet and at least one outlet, said at least one inlet is provided with DME comprising a lubricant from a fuel tank. Said at least one outlet from said first heat exchanger is providing clean DME, and said lubricant is trapped in said first heat exchanger. 
     In still another example embodiment the APU further comprising a second heat exchanger, said second heat exchanger is connected to the exhaust gases from said after burner, said second heat exchanger further comprising at least one inlet and at least one outlet, said at least one inlet is connected to a condenser with condensed water from the fuel cell, said outlet is connected to said fuel processor for providing steam to said fuel processor. 
     In still another example embodiment said first heat exchanger and said second heat exchanger is the same unit. 
     In still another example embodiment said first heat exchanger is heated by gases from a water condenser. 
     In still another example embodiment said first heat exchanger has a DME fuel inlet and DME gas outlet and a lubricant outlet. 
     In still another example embodiment said first heat exchanger has a gas inlet and gas outlet and an outlet for condensed water. 
     In still another example embodiment said first heat exchanger is heated by cooling water from the fuel cell. 
     In still another example embodiment said first heat exchanger has a DME fuel inlet and DME gas outlet and a lubricant outlet. 
     In still another example embodiment said first heat exchanger has a cooling water inlet and cooling water outlet. 
     It is desirable to provide an auxiliary power unit process in which the above mentioned problem with DME mixed with lubricant is at least reduced or eliminated. 
     In a first example embodiment an auxiliary power unit process comprising the actions of providing air, steam and DME fuel to fuel processor unit, extracting at least hydrogen from said fuel processor unit, providing said hydrogen and air to a fuel cell, condensing water extracted from said fuel cell in a condenser, combusting rest fuel from the fuel cell in an after burner, separating a lubricant from a DME fuel before providing said DME fuel to the fuel processor unit. 
     In another example embodiment of the auxiliary power unit process, said separating of DME and lubricant is performed by using exhaust gases from said after burner in a first heat exchanger. 
     In still another example embodiment said first heat exchanger is heated by gases from a water condenser. 
     In still another example embodiment said first heat exchanger has a DME fuel inlet and DME gas outlet and a lubricant outlet. 
     In still another example embodiment said first heat exchanger has a gas inlet and gas outlet and an outlet for condensed water. 
     In still another example embodiment said first heat exchanger is heated by cooling water from the fuel cell. 
     In still another example embodiment said first heat exchanger has a DME fuel inlet and DME gas outlet and a lubricant outlet. 
     In still another example embodiment said first heat exchanger has a cooling water inlet and cooling water outlet. 
     In yet another example embodiment the auxiliary power unit process further comprising the action of providing steam to said fuel processor by heating said water from said condenser in a second heat exchanger heated by said exhaust gases from said after burner. 
     In still another example embodiment of the auxiliary power unit process said first heat exchanger for providing steam is the same heat exchanger as the second heat exchanger for separating the lubricant from the DME fuel. 
     The present invention also relates to a vehicle provided with an engine for traction power, an auxiliary power unit (APU) and a reservoir of fuel. Said fuel is used for running said engine and said APU. Said APU comprising a fuel processor and a fuel cell, wherein said fuel processor is provided between said fuel reservoir and said fuel cell. Said fuel is dimethyl ether (DME), wherein means is provided for separating said DME fuel from at least one lubricant included in said DME. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       With reference to the appended drawings below follows a more detailed description of embodiments of the invention cited as examples. 
       In the drawings: 
         FIG. 1   a  shows a schematic view illustrating a first example embodiment of an APU according to the invention. 
         FIG. 1   b  shows a schematic view illustrating a second example embodiment of an APU according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     In  FIG. 1   a  an APU  100  according to an example embodiment of the invention is schematically illustrated. The APU  100  comprises an optional air compressor  102 , a reformer  104 , a CO clean-up  108 , a fuel cell  122 , an afterburner  124 , a condenser  120 , a first heat exchanger  114  and a second heat exchanger  180 . 
     The first heat exchanger  114  may be used interchangeably with the second heat exchanger  180  in the following text and claims, i.e., they may be the same unit or may change position with each other in the embodiments as illustrated in the figures and the following text. 
     The reformer  104  may have different designs and properties. In a first embodiment said reformer  104  comprises a mix zone and a catalytic converter. The mix zone is arranged at an inlet side of said reformer and the catalytic converter is arranges at an outlet side of the catalytic converter, i.e., said mix zone is arranged prior to said catalytic converter in a direction of flow of gases introduced into the reformer  104 . Said first embodiment of the reformer  104  may be used when the gases to be reformed are not mixed before entering said reformer  104 . In a second embodiment said reformer.  104  is a catalytic converter without a mix zone. The second embodiment of the reformer  104  may be useful when the gases to be reformed are premixed before entering said reformer  104 . The catalytic converter in said reformer  104  may be made of ceramic or metal in the form of a monolithic structure. A catalytic material is attached onto said monolithic structure. Said catalytic material may for instance comprise different palladium-zinc alloy on AI2O3. Said catalytic converter may also be divided into different zones with different properties, i.e., different catalytic materials in different zones and/or different mixtures of two or more catalytic materials in different zones. A catalytic converter divided into zone as just described may be used to favour at least one reaction in a beginning or an end of the catalytic converter and/or to suppress at least a second reaction at the beginning or the end of the catalytic converter. Instead of using a monolithic structure as the bearer of the catalytic material pellets covered at least partially with catalytic material may be used. Said pellets may be in the form of solid bodies in any form for instance spherical or irregular. Said pellets may be made of ceramic material or a metal. Instead of using in the form of solid bodies, porous bodies may be used. Instead of covering the pellets made of non catalytic material at least partly with a catalytic material, said pellets may be made of a catalytic material. 
     Enclosing said pellets or monolithic structure and if present the mixing zone is a body made for instance of steel. Said body may be isolated. The reformer  104  may also be built as a heat exchanger. The temperature inside the reformer  104  may be between 250 C-700 C. 
     The reformer  104  has at least one inlet and at least one outlet. If present, the mixing zone is closest to said inlet and the catalytic converter is closes to the outlet. The reformer  104  is provided with different gases. The reformer  104  is a part of a process of reforming at least one gas into a suitable fuel for the fuel cell. According to an example embodiment of the present invention air, DME and steam are used as input gases into the reformer. In the example embodiment illustrated in  FIG. 1   a , air is provided air a first inlet  172 , DME is provided at a second inlet  174 , and steam is provided at a third inlet  176  of said reformer  104 . In said reformer many different reactions are taking place. Some of the more important reactions are as follows:
 
DME+air: CH3OCH3+3/2 02=&gt;2CO2+3H2  1)
 
DME+steam: CH3OCH3+3H20→2CO2+6H2  2)
 
DME+air: CH3OCH3+1/2O2=&gt;2CO+3H2  3)
 
CO+steam: CO+H20&lt;=&gt;CO2+H2  4)
 
DME+steam: CH3OCH3 H20=&gt;&gt;2CH3OH  5)
 
Methanol+air: CH3OH+V2 02=&gt;CO2+2H2  6)
 
Methanol+steam: CH3OH+H2O=&gt;CO2+3H2  7)
 
Methanol+air: CH3OH+O2→CO+2H20  8)
 
     From the list of reactions above, desired reactions are reaction 1 and 2. The other equations (3-8)+the equations not mentioned are so called secondary reactions which may be suppressed as much as possible. Reaction number 4 is a balance equation which is moved to the right at higher temperatures. 
     From the outlet  178  of the reformer  104  comes inter alia N2, CO, H2, H20 CH4 and traces of other material and/or contaminations from inter alia the air provided at the input of the reformer  104 . 
     In the illustrated embodiment in  FIG. 1   a , air is provided to the first inlet  172  of the reformer via a first pipe  128 , DME is provided to the second inlet  174  of the reformer via a second pipe  126 , and steam is provided to the third inlet  176  of the reformer via a third pipe  130 . Air may be provided into the reformer with an overpressure created by an optional air compressor  102 . In an alternative embodiment said reformer  104  only comprises one inlet for providing the different gases, which may be blended or not depending on the design of the reformer  104 . If the gases are not blended, the above mentioned mixing chamber is in the reformer  104 . 
     The outlet  178  of the reformer  104  is coupled to a first inlet  180  of the CO clean-up device  108  via a fourth pipe  160 . In said fourth pipe  160 , N2, CO, H2, H20 and CH4 from the reformer  104  are transferred to the CO clean-up device  108 . Also provided to the CO clean-up device  108  is air to a second inlet  182  of said CO clean up  108  via pipe  128 , which may or may not be provided with overpressure depending on the presence of the compressor  102 . The CO clean-up device  108  may be built similarly as the reformer  104  with a slight difference in the material chosen for the catalytic converter. In the CO clean-up device  108  said catalytic converter material may be platinum-based. The temperature in the CO clean-up device is between  150 C- 180 C. In one embodiment said CO clean-up device is built as a heat exchanger. Between the reformer  104  and the CO clean-up device  108  a heat exchanger may be provided. 
     A desired reaction taking place in the CO clean-up device  108  is:
 
CO+1/2O2=&gt;CO2  9)
 
     An optional reaction can be H2+1/2O2=&gt;H20 which will consume the hydrogen and is undesired and will lower the total efficiency for the system 
     As the name of the device may suggest said CO clean-up device is used for transforming harmful CO which is present in the gases coming from the reformer  104  into less harmful CO2. 
     An output  184  of the CO clean-up device  108  is connected to a first inlet  186  of the fuel cell  122  via a fifth pipe  150 . Air is also provided to a second inlet  188  of the fuel cell  122  via the first pipe  128 . Depending on the presence of the air compressor  102  said air is provided to the fuel cell  122  with overpressure or not. Gases provided to the fuel cell  122  is air and the gases produced in the reformer 1.04 minus all or part of the CO content which is transformed into CO2 in the CO clean-up device  108 . The reaction taking place in the fuel cell  122  is:
 
H2+1/2O2→H20.  10)
 
     Said reaction is taking place on electrodes, where electrons are moving in wires and hydrogen ions are moving through an electrolyte membrane which separates the hydrogen gas from the air. 
     The fuel cell  122  has a first cooling pipe  154  and a second cooling pipe  156 . In one of said first of second cooling pipes  154 ,  156  a coolant is provided to the fuel cell. In the other cooling pipe  156 ,  154  said coolant is transferred from the fuel cell. Said first and second cooling pipes  154 ,  156  may be coupled to a radiator not illustrated in  FIG. 1   a . The coolant may be air, water, AC coolant such as R-134A, or any other suitable coolant. Said coolant may be used in a heat exchanger arrangement  1000  as shown in phantom in  FIG. 1   a  for separating the lubricant from the DME fluid. Another useful application of the coolant is to use its heat for heating the driver compartment. Another useful application of the heat is to transfer it to and through the engine and/or a cooling system for the engine in order to keep said engine warm while not running the engine. 
     An output  190  of the fuel cell  122  is connected to an inlet  192  of the condenser  120  via pipe  140 . In said condenser  120 , water is condensed to the bottom of said condenser  120  and separated from the rest of the gases coming from the fuel cell  122 . Not all of the hydrogen provided to the fuel cell  122  via the fifth pipe  150  is consumed and transformed into water and energy in the fuel cell  122 . The hydrogen which is not consumed in the fuel cell  122  (together with other gases not fully consumed in the fuel cell  122 , inter alia methane), so called rest fuel, are transferred to an inlet  196  of the after burner  124  via pipe  134 . 
     The after burner or combustor  124  may be constructed in similarity to the CO clean up device  108 . The material in the catalytic converter may be a catalyst of Noble metal and/or base metals supported on a monolith. 
     The heat produced by the after burner  124  when combusting the rest fuel from the fuel cell  122  is used to make steam of the water coming from the condenser  120 . From an outlet  198  of the combustor  124  is combusted gas transferred to a first inlet  181  of the heat exchanger  114  via pipe  132 . Water from the condenser  120  is transferred from a first outlet  197  of the condenser  120  to a second inlet  194  of the first heat exchanger  114  via pipe  138 . The heat of the combusted gas in the first heat exchanger  114  is heating the water to and above its boiling point in order to produce steam. Said steam from the first heat exchanger is transferred from a second outlet  183  to said third inlet  176  of the reformer  104  via said third pipe  130 . 
     In the embodiment of the invention illustrated in  FIG. 1   a , a first inlet  189  of the second heat exchanger  180  is coupled to a first outlet  185  of the first heat exchanger  114  via a pipe  170 . In said pipe  170  combusted gases from the combustor  124 , which has passed through the first heat exchanger  114 , is provided to the second heat exchanger  180 . DME is fed to a second inlet  193  of said second heat exchanger  180  via pipe  190 . Said DME is separated from a lubricant within said second heat exchanger  180 . Said lubricant may be trapped in said second heat exchanger  180  or fed to the after burner for combustion. DME, which is pure and free from lubricant, is fed to the reformer  104  via a second pipe  126 , which is connected between a second outlet  187  of said second heat exchanger  180  and the second inlet  174  of said reformer  104 . 
     Combusted gases are transferred out of said second heat exchanger  180  via a first outlet  191 . 
     In an alternative embodiment the first and second heat exchangers  114 ,  180  are the same unit. 
     The temperature in the reformer  104  may be between 350° C.-450° C. The temperature in the CO clean-up device  108  may be between 150° C.-180° C. The temperature in the Fuel cell  122  may be around 80° C. The temperature in the condenser  120  may be 80° C.-50° C. The temperature in the combustor may be between 400° C.-500° C. The temperature of the water before the first heat exchanger  114  may be less than 50° C. The temperature of the steam after the first heat exchanger may be above 140° C. The temperature of the combusted gas before the first heat exchanger may be 400° C.-500° C. The temperature of the combusted gas after the first heat exchanger may be 50° C.-200° C. 
     In  FIG. 1   b  an alternative example embodiment of the present invention is illustrated. This embodiment differs compared to the embodiment illustrated in  FIG. 1   a  in that it comprises a water gas shift  106 , a third heat exchanger  112 , a fourth heat exchanger  110  and a water tank  118 . It further differs in that the second heat exchanger  180  is connected in a somewhat different manner. The water gas shift  106  is connected with a first inlet  115  to the outlet  178  of the reformer with the pipe  160 . An outlet  117  of said water gas shift  106  is connected to a first inlet  119  of the third heat exchanger  112 . A first outlet  135  of said third heat exchanger  112  is connected to the first inlet  180  of the CO clean-up device  108 . A first inlet  127  of the water tank is connected to the first outlet  197  of the condenser  120 . A first outlet  129  of the water tank is connected to a first inlet  139  of the fourth heat exchanger  110  via pipe  158 . A second outlet  131  of said water tank  118  is connected to the first inlet  115  of the water gas shift  106  via pipe  144 . A first outlet  137  of said forth heat exchanger  110  is connected to a second inlet  121  of the third heat exchanger  112  via pipe  146 . A second outlet  133  of said third heat exchanger  112  is connected to the second inlet  194  of the first heat exchanger  114  via pipe  148 . The outlet  194  of CO clean-up device  108  is connected to a second inlet  123  of the forth heat exchanger  110  via pipe  150 . The second outlet  125  of said fourth heat exchanger  110  is connected to the first inlet  186  of the fuel cell  122  via pipe  152 . 
     In the embodiment as illustrated in  FIG. 1   b , the rest gases from the fuel cell  122  is lean of hydrogen due to the set up of cold water injection into the water gas shift  106 , the third heat exchanger  112  and fourth heat exchanger  110 . The third heat exchanger  112  and the fourth heat exchanger  110  are cooling the gases introduced into the fuel cell  122  and increasing the water/steam content in the same gases. 
     A lower hydrogen content in the rest gases requires that the temperature of said gases are elevated compared to if the hydrogen content is higher as it is in the embodiment illustrated in  FIG. 1   a . Increased rest gas temperature is performed by heating said gases in the second heat exchanger  180 , i.e., the gases introduced in the after burner  124  are heated by the exhaust gases from the after burner  124  in said second heat exchanger  180 . 
     The temperature in the water gas shift may be around 250° C.-350. 
     In the embodiment as illustrated in  FIG. 1   b  the steam provided to the reformer  104  is heated in three steps. A first step is in the fourth heat exchanger  110 , a second step is in the third heat exchanger  112  and a third step is in the first heat exchanger  114 . 
     In another example the first heat exchanger, which separates the DME fuel from the lubricant, is heated by the gases from the water-condenser. In this example the water condenser is working at some higher temperature and the last water is condensed by rejecting heat to the DME fuel. 
     It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.