Calcium looping process for high purity hydrogen production integrated with capture of carbon dioxide, sulfur and halides
A process for producing hydrogen comprising the steps of: (i) gasifying a fuel into a raw synthesis gas comprising CO, hydrogen, steam, sulfur and halide contaminants in the form of H 2 S, COS, and HX, wherein X is a halide; (ii) passing the raw synthesis gas through a water gas shift reactor (WGSR) into which CaO and steam are injected, the CaO reacting with the shifted gas to remove CO 2 , sulfur and halides in a solid-phase calcium-containing product comprising CaCO 3 , CaS and CaX 2 ; (iii) separating the solid-phase calcium-containing product from an enriched gaseous hydrogen product; and (iv) regenerating the CaO by calcining the solid-phase calcium-containing product at a condition selected from the group consisting of: in the presence of steam, in the presence of CO 2 , in the presence of synthesis gas, in the presence of H 2 and O 2 , under partial vacuum, and combinations thereof.
1. A process for producing hydrogen, comprising the steps of:
reforming in a reforming unit a gaseous hydrocarbon fuel in the presence of calcium oxide and steam to remove carbon dioxide, sulfur and halide contaminants that are present in the form of H 2 S, COS and HX, wherein X is a halide, thereby forming a solid-phase calcium-containing product comprising CaCO 3 , CaS and CaX 2 , and producing a mixture of carbon monoxide and hydrogen;
separating the solid-phase calcium-containing product from an enriched gaseous hydrogen product;
regenerating the calcium oxide to produce a calcined sorbent by calcining the solid-phase calcium-containing product at a condition selected from the group consisting of: in the presence of steam, in the presence of carbon dioxide, in the presence of synthesis gas, in the presence of hydrogen and oxygen, under partial vacuum, and combinations thereof;
reactivating the calcined sorbent by hydrating it in the presence of steam or water or a mixture of both; and
injecting the hydrated sorbent into the reforming unit.
2. The process of claim 1 additionally comprising the step of:
recycling at least a portion of a product stream from a Fischer-Tropsch reactor, fed by the reformer, so as to introduce a chemical species selected from the group consisting of: methane, C1-C4 hydrocarbons, carbon dioxide, hydrogen and combinations thereof back into the reformer.
3. The process of claim 2 wherein the reforming step is conducted in the presence of a catalyst.
4. The process of claim 1 wherein the enriched hydrogen product has a purity in the range of from about 70% to about 99.99% H 2 , a temperature in the range of from about 400 to about 1000° C., and a pressure in the range of from about 1 to about 100 atmosphere.
5. The process of claim 1 wherein the calcium oxide has a sorption capacity of at least 30 grams of carbon dioxide per kilogram of calcium oxide for 5 cycles and higher.
6. The process of claim 1 , comprising of a fixed fluidized bed of catalyst particles with the calcium sorbent entrained through the system.
7. The process of claim 1 wherein the heat produced by the exothermic production of CaCO 3 from carbon dioxide and calcium oxide is used for the endothermic reforming step.
8. The process of claim 1 wherein the reforming step is conducted in the presence of a reforming or prereforming catalyst.
9. The process of claim 8 wherein the catalyst is selected from the group consisting of: Ni, Pt, Rh, Pd, Ru, W, Mo, their oxides, their carbides and their sulfides.
10. The process of claim 8 wherein the calcium oxide is mixed with the reforming or a prereforming catalyst and the hydrogen is produced at a temperature in the range of 550-750° C., and a pressure in the range of 1-60 atmospheres.
11. The process of claim 10 , wherein the pressure is in the range of from 20 to 30 atmospheres.
12. The process of claim 10 , wherein the temperature is in the range of 600-700° C.
13. The process of claim 12 , wherein the pressure is in the range of from 20 to 30 atmospheres.