Process for staged combustion of retorted oil shale

A process for combusting crushed retorted particles containing combustible materials comprising sulfur and nitrogen-containing compounds by staged combustion, said staged combustion comprising:

• (1) combusting a substantial proportion of the combustible material contained within said particles by staged combustion, said staged combustion comprising:
• (a) combusting said particles in a first-stage fluidized combustion zone having a dense bed, the particles being maintained as a fluidized bed by a fluidizing gas stream comprising oxygen introduced into said first-stage combustion zone at a rate sufficient to maintain said particles as a fluidized bed while providing a substoichiometric quantity of oxygen for combustion of said combustible material in said first-stage combustion zone;
• (b) combusting off-gases from said first-stage combustion zone in a second-stage combustion zone, with combustion being maintained by a gas stream comprising oxygen introduced into said second-stage combustion zone, said combustion being under conditions sufficient to produce a flue gas of relatively low carbon monoxide, nitrogen oxides, and sulfur oxides content;
• (2) controlling the flow of said fluidizing gas stream so as to maintain the concentration of gaseous ammonia in said first-stage fluidized combustion zone below about 100 ppm by volume;
• (3) discharging said flue gas from said second-stage combustion zone;
• and
• (4) discharging crushed particles in a relatively decarbonized condition from said first-stage combustion zone.

A process for combusting crushed retorted particles containing combustible materials comprising sulfur and nitrogen-containing compounds by staged combustion, said staged combustion comprising:

• (1) combusting a substantial proportion of the combustible material contained within said particles by staged combustion, said staged combustion comprising:
• (a) combusting said particles in a first-stage fluidized combustion zone, the particles being maintained as a fluidized bed by a fluidizing gas stream comprising oxygen introduced into said first-stage combustion zone at a rate sufficient to maintain said particles as a fluidized bed while providing a substoichiometric quantity of oxygen for combustion of said combustible material in said first-stage combustion zone, said fluidized bed having a dense bed region;
• (b) combusting off-gases from said first-stage combustion zone in a second-stage combustion zone, with combustion being maintained by a gas stream comprising oxygen introduced into said second-stage combustion zone, said combustion being under conditions sufficient to produce a flue gas of relatively low carbon monoxide, nitrogen oxides, and sulfur oxides content;
• (2) controlling the flow of said fluidizing gas stream so as to maintain the concentration of gaseous ammonia in the dense bed region of said fluidized bed below about 100 ppm by volume;
• (3) discharging said flue gas from said second-stage combustion zone;
• and
• (4) discharging crushed particles in a relatively decarbonized condition from said first-stage combustion zone.

A process for combusting crushed retorted shale particles of a size suitable for fluidization, said shale particles containing combustible materials comprising sulfur and nitrogen-containing components and components capable of reacting with gaseous sulfur components in step 1 (a) hereinafter to produce stable solid sulfur-containing materials, which process comprises:

• (1) combusting a substantial proportion of the combustible material contained within said shale particles by staged combustion, said staged combustion comprising:
• (a) combusting said particles in a first-stage fluidized combustion zone, the particles being maintained as a fluidized bed by a fluidizing gas stream comprising oxygen introduced into said first-stage combustion zone at a rate sufficient to maintain said particles as a fluidized bed while providing a substoichiometric quantity of oxygen for combustion of said combustible material in said first-stage combustion zone, said first-stage combustion zone having a dense bed region;
• (b) combusting off-gases from said first-stage combustion zone in a second-stage combustion zone, combustion being maintained therein by a gas stream comprising oxygen introduced into said second-stage combustion zone, said combustion being sufficient to produce a flue gas of relatively low carbon monoxide, nitrogen oxides, and sulfur oxides content;
• (2) discharging said flue gas from said staged combustion;
• (3) discharging crushed particles in a relatively decarbonized condition from said staged combustion;
• (4) maintaining the concentration of gaseous ammonia in the dense bed region of said first-stage fluidized combustion zone between about 50 and about 100 ppm by volume, said concentration of gaseous ammonia being controlled by adjusting the amount of oxygen in said fluidizing gas stream;
• (5) maintaining the concentration of gaseous carbon monoxide in said flue gas to less than about 500 ppm by volume by adjusting the amount of oxygen in said gas stream;
• (6) feeding decarbonized fines of shale particles at a relatively cool temperature into the dense bed region of said first-stage combustion zone to aid in controlling temperature during staged combustion below a peak value between about 1400.degree. and about 1670.degree. F., said decarbonized fines of shale comprising no more than 50 percent by weight of the total shale particles introduced into said first-stage combustion zone;
• and
• (7) introducing inert diluent gas into said fluidizing gas stream to aid in controlling temperature during staged combustion below said peak value while maintaining said shale particles as a fluidized bed.