US 6,083,862 AGranted

Cyclic process for oxidation of calcium sulfide

AssigneeIowa State University Research Foundation, Inc.

InventorThomas D. Wheelock

Life of this patent

Estimating the term…

Loading patent…

Abstract

Calcium sulfide particles in mixtures with carbon particles, as in coal gasifier waste, are converted to calcium oxide by repeated cycles of oxidation and reduction by utilizing the carbon as a source of the reducing gas required for the treatment. The treatment can be conducted in a two zone fluidized bed reactor by limiting the amount and concentration of oxygen supplied to a lower reducing zone and by supplying excess oxygen to an upper oxidizing zone. Alternatively, for particles less than 0.5 mm in size, the treatment can be conducted by utilizing either two transport reactors or two circulating fluidized bed reactors in series whereby the first reactor in the series is maintained in a reducing state and the second reactor is maintained in an oxidizing state. The particles are transported sequentially through both reactors and recycled several times. The amount and concentration of oxygen supplied to the first reactor is limited to create reducing conditions, while excess oxygen is supplied to the second reactor to create oxidizing conditions.

Claims23

Dependent claims

A process for oxidizing calcium sulfide, said process comprising the steps of:

exposing particles contained in waste solids produced by coal gasification comprising calcium sulfide and a source of carbon in a fluidized bed reactor having an upper part, a lower part, a middle part, and a bottom, to a treatment cycle conducted at a temperature within a temperature range greater than 900.degree. C. by circulating said particles freely between the lower part of the fluidized bed reactor maintained in a reducing state and the upper part of the fluidized bed reactor maintained in an oxidizing state so that said particles are treated repeatedly to oxidation and reduction;
creating reducing conditions of said reducing state in the lower part of the fluidized bed reactor by supplying oxygen in a fluidizing gas to the bottom of the fluidized bed reactor in an amount less than 50% of the stoichiometric amount required for complete combustion of the carbon in feed particles comprising calcium sulfide and carbon, wherein incomplete combustion of the carbon supplies carbon monoxide and hydrogen reducing gases, and wherein the concentration of oxygen in said fluidizing gas is less than 10 volume %;
and
creating oxidizing conditions of said oxidizing state in the upper part of the fluidized bed by introducing additional air in the middle of the fluidized bed in an amount such that oxygen supplied to the fluidized bed reactor exceeds the sum of a stoichiometric amount required for complete combustion of the carbon in the feed particles and a stoichiometric amount required for complete conversion of calcium sulfide to calcium oxide and sulfur dioxide.

1 more element

A process for oxidizing calcium sulfide, said process comprising the steps of:

exposing particles contained in waste solids produced by coal gasification comprising calcium sulfide and carbon to a treatment cycle conducted at a temperature of at least 900.degree. C. in a reaction system comprising a first chemical reactor and a second chemical reactor in series, wherein the first chemical reactor is maintained in a reducing state and the second chemical reactor is maintained in an oxidizing state by introducing feed particles comprising calcium sulfide and carbon into the first chemical reactor and, after treatment in the first chemical reactor, passing treated particles to the second chemical reactor and, after treatment in the second chemical reactor, returning subsequently treated particles to the first reactor for further treatment;
and
repeating said treatment cycle at least two times before the particles are removed from the reaction system;
creating reducing conditions in the first chemical reactor by supplying the first chemical reactor with air in such an amount that oxygen is supplied in a quantity of less than 50% of a stoichiometric amount required for complete combustion of the carbon in the feed particles, wherein incomplete combustion of the carbon supplies carbon monoxide and hydrogen reducing gases;
and
creating oxidizing conditions in the second chemical reactor by supplying the second chemical reactor with air such that a sum of oxygen supplied to the first chemical reactor and oxygen supplied to the second chemical reactor exceeds both a stoichiometric amount of oxygen required for complete oxidation of the carbon in the feed particles and a stoichiometric amount of oxygen for complete conversion of calcium sulfide in the feed particles to calcium oxide and sulfur dioxide.

3 more elements

Dependencies are inferred from the claim text.

Facts

Application: 08/903,291Filed 30 Jul 1997 · continuation in part
Priority: 14 Mar 1994
Granted: 4 Jul 2000
Term ends: Not estimatedThe source records don’t support an estimate.

Classification5 codes

C01B 17/508
Preparation of sulfur dioxide: by oxidation of sulfur compounds
C01F 11/08
Oxides or hydroxides: by reduction of sulfates
C01F 11/10
Oxides or hydroxides: from sulfides
C01B
Non-metallic elements

Family

Serial209,734Parent of this continuation-in-part · filed 14 Mar 1994
Serial468,841Parent of this continuation-in-part · filed 6 Jun 1995
US 5,653,955 AParent of this continuation-in-part
US 5,433,939 AParent of this continuation-in-part
US 6,083,862 AThis patent

From the US filing history. Foreign family members aren’t listed.