Method for producing electricity and heat

0001The invention relates to a method for generating electricity and heat, in particular a method in which a high-temperature fuel cell and combined with a gas turbine is used.

State of the art

0002The power generation by means of chemical energy is happen in the long term by means of fuel cells, because the electrochemical Energy conversion the highest efficiencies allows. As in high temperature fuel cells, a significant Proportion of the energy used in high-temperature heat is converted, it is obvious that these thermal in a also convert process into electrical energy and thus the entire process in its efficiency again sustained increase. This case, the Joule process to which in open gas turbines in the conventional Power plant technology, in particular in gas-steam combined-cycle plants, has been used for some time.

0003The combination of gas turbines and fuel cells, especially of high-temperature fuel cell, at time extensively studied and developed. In this concepts the gas turbine is always operated with a combustion chamber, which is under a higher than atmospheric pressure. The compressor draws in the air from the atmosphere and compressed it to a higher pressure. It warms the Air. It is then fed to the fuel cell. The Fuel cell has higher pressure within the cell stack a higher cell voltage. As a result, their performance be increased. Since in the high-temperature fuel cell the fuel only in an amount of usually 80% or burns less, makes sense, the residual fuel quantity, the leaves with the exhaust gas, the fuel cell, in burn the combustion chamber of the gas turbine and the completely increasing temperature of the medium.

0004This principle of combination of gas turbine and fuel cell is associated with some significant problems. To set the pressure and the high temperature level within the cell stack high demands on the Components and materials. In most gas turbines is the Temperature is not emerging from the air compressor high enough to meet the requirements of an optimal operation To meet within the fuel cell. You must therefore preheated will. This reduces the efficiency of the overall system. The turbine exhaust is mostly too low Temperature as a heat source for preheating the air to become.

0005It follows that the combination of conventional gas turbines afflicted with high temperature fuel cells with handicaps is, in the thermodynamic design of the gas turbine process founded are:<ul><li>high pressure in the cell stack leads to constructive regularly problems,</li><li>high turbine inlet temperature often requires more Fuel input in the combustor as the fuel cell of is supplied by fuel slip,</li><li>the temperature at the compressor outlet is regularly low, usually has the air through extra Fuel expenses are heated.</li></ul>

Problem and Solution

0006The object of the invention is a method for producing provide electricity and heat, which the aforesaid Disadvantages of the prior art overcomes. Further it is an object of the invention to provide a device, with which the aforementioned method can be carried out. The objects of the invention are achieved by a method with all the characteristics according to the main claim, and by a method according to independent claim. advantageous Find embodiments of the method and apparatus respectively in the subsequent dependent claims again.

The invention

0007The inventive method for generation of electricity and Heat based on a method in which a fuel cell, in particular a high-temperature fuel cell, and a gas turbine are coupled together. Different to common but is used in the combustor of the gas turbine with Air worked under atmospheric pressure. For the purposes of this invention is atmospheric pressure as a pressure between 1 and 2 bar defined, which means also a slight overpressure is to be included even with the term atmospheric pressure. Setting from atmospheric pressure in the combustion chamber has the advantage that the material requirements for the coupled Fuel cell stack for normal conditions and not must be designed for high compressive strength.

0008In an advantageous embodiment of the method is the of the fuel cell air supplied first by the exhaust gases the gas turbine is preheated.

0009In a further variant of the method is from the combustion chamber exiting, located under atmospheric pressure Gas in the turbine in a vacuum, such as 0.2 to 0.4 bar, relaxed, and then the compressor back to ambient pressure (atmospheric pressure) compressed. This process variant has the advantage, that the Pressure in the combustion chamber and the fuel cell about be maintained at atmospheric level, or up to 2 bar can, which to a significantly simpler design This process component leads.

0010As beneficial has also been found, the exhaust gas from to direct the turbine through a heat exchanger (recuperator) in which the temperature of the exhaust gas is reduced and the withdrawn amount of heat for preheating the supply air for the Fuel cell is used. Among a recuperator a heat exchanger in the exhaust stream for the recovery of waste heat to understand. This advantageously facilitates the efficiency of the Procedure increased because an external preheat the incoming air for the fuel cell is omitted.

0011Furthermore, in the inventive method of Advantageous if the preheated in the recuperator airflow in two subsets is divided, of which a part of the The fuel cell is supplied as the supply air and another Part is supplied to the exhaust stream of the fuel cell. On Thus, in particular the composition of the air in the gas turbine combustor with respect to the remaining portion of fuel be varied.

0012The advantages of the process according to the invention can be summarized as follows:<ul><li>The gas turbine heats the combustion air by means of recuperator applicable before that it directly to the fuel cell can be supplied. It eliminates an additional Heating of the air before entry into the fuel cell.</li><li>The air is at atmospheric pressure, ie the cell stack must not be flameproof. Should the Pressure in the fuel cell and in the combustion chambers of slightly be higher than 1 bar, eg., 1.5 or 2 bar, the air is already prior to entry into the recuperator pre-compressed to the desired pressure. </li><li>The gas turbine combustion chamber, by changing the bypassed air (7) a variable residual fuel in the exhaust gas the fuel cell can be adapted in a simple manner.</li><li>The entire system can also for small system sizes very high efficiencies, z. B.> 70%, reaching.</li></ul>

0013In a further embodiment of the method, the heat from the boiler to produce saturated steam of 1 use bar. This is injected into the combustion chamber. Thus, the mass flow increases in the turbine. in the same proportion increases the turbine output. By the cooling of the exhaust gas before entry into the compressor the previously injected water vapor is precipitated again and the compressor is not with the additional mass flow loaded. This variant allows the electrical Of the gas turbine and thus the performance of the entire system increase.

SPECIFIC DESCRIPTION

0014Subsequently, the subject of the invention with reference to a Embodiment described in more detail in the form of a figure, without the subject matter of the invention is limited by becomes. In the figure mean:<dl tsize="2" compact="compact"><dt>1</dt><dd>fuel cell</dd><dt>2</dt><dd>fuel</dd><dt>3</dt><dd>Outside air intake</dd><dt>4</dt><dd>recuperator</dd><dt>5</dt><dd>Preheated air</dd><dt>6</dt><dd>Supply air to the fuel cell</dd><dt>7</dt><dd>bypass air</dd><dt>8th</dt><dd>Exhaust gas from the fuel cell</dd><dt>9</dt><dd>Residual fuel from the fuel cell</dd><dt>10</dt><dd>Mixed gas before the combustion chamber</dd><dt>11</dt><dd>combustor</dd><dt>12</dt><dd>Exhaust gas from the combustion chamber</dd><dt>13</dt><dd>turbine</dd><dt>14</dt><dd>Exhaust gas from the combustion chamber</dd><dt>15</dt><dd>Exhaust gas from the recuperator</dd><dt>16</dt><dd>exhaust gas cooler</dd><dt>17</dt><dd>Exhaust gas at the compressor inlet</dd><dt>18</dt><dd>compressor</dd><dt>19</dt><dd>in the compressor to ambient pressure compressed gas</dd><dt>20</dt><dd>waste heat boiler</dd><dt>21</dt><dd>Engine exhaust into environment</dd></dl>

0015The basic scheme of the new process is shown in the figure. The outside air (3) enters the recuperator a (4). There it is heated from 15 c to z. B. 600 ° (5). Before entering in the fuel cell (1), a bypass flow (7) diverted. The residual air flow (6) occurs in parallel to the fuel (2) into the fuel cell. There is a part of the Atmospheric oxygen for electrochemical reaction of the fuel consumed. The remaining oxygen in the air shall meet with the anode exhaust gas from the fuel cell from. anode exhaust gas (9) with excess air from the fuel cell and / or cathode exhaust (8) with excess remaining Air oxygen are mixed with the bypass air (10) and enter the combustion chamber (11).

0016With the residual fuel from the fuel cell, which in Anode waste gas (9) is contained, the air in the combustion chamber is heated to the temperature at the turbine Entry is needed (12), z. B. 930 ° C. The system pressure in all stages of the process described above corresponds in approximately the ambient pressure.

0017In the turbine (13) the hot exhaust gas from the combustion chamber bar laid of about 1 bar on z. B. 0.33. It cools off the gas to about 660 ° C. It flows through the recuperator and cooled to an outlet temperature of about 80 ° C. (17). The heat output is the temperature increase of the outside air (from 15 to 600 ° C). To the exhaust so far as cooling is possible, it goes through another Heat exchanger / cooler (16), so that the exhaust gas (17) For example, setting temperatures around 30 ° C. With this Temperature is the exhaust gas at a pressure of about 0.3 bar sucked in by the compressor (18) and compressed to ambient pressure (19). It heats up to about 180 ° C. Before it is released into the environment, the exhaust gas in a heat recovery is (20) are cooled. The recovered heat can advantageously be used to supply a heating system will.