Electrolyzer Systems and Operation Thereof

Abstract

Conventional control schemes for electrolyzers focus on maximizing electrical efficiency, which describes the relationship between the electrical energy consumed and the gas produced by the electrolyzer. However, the cost associated with high electrical efficiency may be unnecessarily expensive. In one embodiment presented herein, a model is used to determine the cost (or profit) associated with a gas produced by the electrolyzer at each of a plurality of operating conditions. The control system can select the operating condition to use based on which operating condition is associated with the lowest cost (or highest profit), even though that operating condition may not be associated with the highest electrical efficiency.

What is claimed is: 
     
         1 . An alkaline electrolyzer system comprising:
 a power input to receive power from an external power source;   an electrolyzer cell comprising a cathode coupled to the power input, an anode coupled to the power input, and a diaphragm at least partially disposed between the anode and the cathode, wherein the electrolyzer cell is configured to (i) use power from the power input to produce a first stream comprising oxygen gas and a second stream comprising hydrogen gas from an alkaline solution, and (ii) operate at a temperature in excess of 120 degrees Celsius (° C.);   a gas separator configured to separate out one or more gasses from the second stream, wherein the one or more second gasses comprises the hydrogen gas;   at least one pump configured to circulate the alkaline solution through the electrolyzer cell;   at least one fluid conduit coupled between the pump and the electrolyzer cell and configured to carry the alkaline solution; and   thermal insulation at least partially covering the electrolyzer cell and the at least one fluid conduit.   
     
     
         2 . The alkaline electrolyzer system of  claim 1 , further comprising:
 a heater configured to heat the alkaline solution prior to the alkaline solution entering the electrolyzer cell.   
     
     
         3 . The alkaline electrolyzer system of  claim 1 , wherein the thermal insulation comprises one or more first pieces of thermal insulation at least partially covering the electrolyzer cell and one or more second pieces of thermal insulation at least partially covering the at least one fluid conduit. 
     
     
         4 . The alkaline electrolyzer system of  claim 1 , further comprising:
 a heat exchanger configured to transfer heat from one or both of the first and second streams to the alkaline solution.   
     
     
         5 . The alkaline electrolyzer system of  claim 1 , further comprising an electrolyzer cell stack that comprises:
 a first end plate;   a second end plate; and   a plurality of electrolyzer cells disposed between the first end plate and the second end plate, wherein the plurality of electrolyzer cells comprises the electrolyzer cell.   
     
     
         6 . The alkaline electrolyzer system of  claim 5 , wherein the anode is a first anode, the cathode is a first cathode, the diaphragm is a first diaphragm, and the electrolyzer cell stack further comprises:
 a second anode;   a second cathode;   a second diaphragm disposed between the second anode and the second cathode;   a gas separation plate disposed between the first cathode and the second anode;   a first channel disposed between the first end plate and the first anode, the first channel having a first channel width;   a second channel disposed between the first anode and the first cathode, the second channel having a second channel width that is smaller than the first channel width; and   a third channel disposed between the first cathode and the gas separation plate, the third channel having a third channel width that is larger than the second channel width.   
     
     
         7 . The alkaline electrolyzer system of  claim 6 , wherein the plurality of electrolyzer cells are connected in series. 
     
     
         8 . The alkaline electrolyzer system of  claim 7 , wherein the electrolyzer cell stack comprises an electrical conductor that electrically connects the first cathode to the second anode, and wherein the electrical conductor passes through the gas separating plate. 
     
     
         9 . The alkaline electrolyzer system of  claim 1 , further comprising:
 a power supply coupled to the power input and configured to induce a pulsed current between the cathode and the anode of the electrolyzer cell that varies based on a control signal.   
     
     
         10 . The alkaline electrolyzer system of  claim 9 , further comprising:
 at least one processor; and   at least one non-transitory computer-readable medium comprising program instructions that are executable by the at least one processor such that the at least one processor is configured to:
 determine at least one characteristic for the pulsed current to be induced between the cathode and the anode, the at least one characteristic for the pulsed current including a frequency of pulses; and 
 generate the control signal for the power supply based on the determined at least one characteristic for the pulsed current. 
   
     
     
         11 . The alkaline electrolyzer system of  claim 1 , further comprising:
 at least one processor; and   at least one non-transitory computer-readable medium comprising program instructions that are executable by the at least one processor such that the at least one processor is configured to:
 generate a cost estimate for hydrogen gas produced by the alkaline electrolyzer system for each of a plurality of different operating states of the alkaline electrolyzer system; 
 select one of the plurality of different operating states based on the generated cost estimates; and 
 control the alkaline electrolyzer system to operate according to the selected operating state. 
   
     
     
         12 . A method of operating an alkaline electrolyzer system, the method comprising:
 causing a temperature of an alkaline solution to rise to a target temperature that exceeds 120 degrees Celsius (° C.);   circulating the alkaline solution through an electrolyzer cell comprising a cathode, an anode, and a diaphragm at least partially disposed between the anode and cathode;   producing a first stream comprising oxygen gas and a second stream comprising hydrogen gas at least in part by inducing a current between the cathode and the anode in the electrolyzer cell;   while producing the first stream and the second stream, operating the electrolyzer at the temperature that exceeds 120° C.;   separating the hydrogen gas from the second stream; and   outputting the hydrogen gas.   
     
     
         13 . The method of  claim 12 , further comprising:
 causing a pressure on the alkaline solution to rise to a target pressure value that exceeds 8 bar.   
     
     
         14 . The method of  claim 12 , further comprising:
 transferring heat from at least one of the first stream and the second stream to the alkaline solution.   
     
     
         15 . The method of  claim 12 , further comprising:
 dynamically determining a frequency of pulses of current that will reduce an impedance of an electrolyzer cell in the electrolyzer system.   
     
     
         16 . The method of  claim 15 , wherein inducing the current between the cathode and the anode in the electrolyzer cell comprises inducing pulses of current at the determined frequency between the cathode and the anode of the electrolyzer cell. 
     
     
         17 . The method of  claim 12 , further comprising:
 while producing the first stream and the second stream,
 (i) identifying a cost associated with at least one feedstock of the electrolyzer system; 
 (ii) for each of a plurality of operating states for the electrolyzer system, estimating a cost associated with the hydrogen gas based on the identified cost associated with the at least one feedstock; 
 (iii) identifying a target operating state for the electrolyzer system based on the estimated cost associated with the hydrogen gas for each of the plurality of operating states; and 
 (iv) controlling at least one controllable component of the electrolyzer system based on the target operating state. 
   
     
     
         18 . A diaphragm for an alkaline electrolyzer having a maximum operating temperature over 120 degrees Celsius (° C.), the diaphragm comprising:
 a support structure comprising at least one of polyetheretherketone (PEEK) or polytetrafluoroethylene (PTFE), the support structure having a thickness of no more than  350  microns between a first side and a second side that is opposite the first side; and 
 a ceramic material disposed on each of the first side and the second side of the support structure, wherein the ceramic material comprises at least one of aluminum oxide (Al2O3) or zirconium dioxide (ZrO2). 
 
     
     
         19 . The diaphragm of  claim 18  wherein the ceramic material is constructed as a ceramic fiber. 
     
     
         20 . The diaphragm of  claim 18 , wherein the support structure comprises a single layer.