Carbonizer (mild gasification)The carbonizing reactor includes two cyclones, the feed system, and a natural gas preheat burner. The carbonizer can be operated as a spouting- or bubbling-bed reactor with a feed capacity of 100 lb/hr at temperatures from 900° to 1650°F and steam partial pressures from 0% to 60%. This design was chosen based on favorable results with caking coals in the COALCO and KRW (Kellogg Rust Westinghouse) gasifier systems. The operative principle allowing the use of caking coal in this reactor is the dilution of the entering coal by an internal recycle of char back to the bottom of the tapered bed, where high velocity and low bed density also reduce agglomeration. A similar regime existed in the 400-lb/hr fast fluidized-bed Perry carbonizer previously used with caking coals at the Grand Forks Energy Technology Center, Grand Forks, North Dakota. The body of the carbonizer consists of four 5-ft-tall sections. The modular design of the carbonizer allows removal of different sections to obtain a variety of gas and char residence times.
The lower two sections are constructed of 24-in. 304L stainless steel (SS) pipe. The pipe is lined with 5.25 in. of insulating refractory and a layer of hard, abrasion-resistant refractory, resulting in a 10-in. i.d. The two upper sections are constructed of 30-in. 304L SS pipe. The pipe is lined with 4.625 in. of insulating refractory and 2 in. of hard refractory, resulting in a 16-in. i.d.
When operated in spouting-bed mode, the smaller diameter of the lower sections of the reactor is intended to increase the velocity and turbulence of the bed and, thus, reduce agglomeration of the test coals. When the high-velocity gas jet enters the larger-diameter upper section, its velocity decreases. The char entrained in the gas jet falls back into the lower section and dilutes the fresh coal entering the bottom of the reactor, providing a longer residence time for the char.
The fluidization gases can be heated by a stoichiometrically operated natural gas burner. The desired operating temperature is maintained by adding air and/or steam or nitrogen to the burner gas in the carbonizer plenum. The char can be removed from the system and cooled in a nitrogen-purged tote bin. The char fines entrained by the gases leaving the top of the carbonizer are separated from the gas stream by a pair of cyclones. The primary cyclone removes particles greater than 10.7 µm in size with 50% efficiency.
The cyclones are constructed of 304 SS pipe. Refractory was cast inside the pipes to form the cones at the bottoms of the cyclones. The fines are removed from the hot-gas stream by the cyclones and collected in a lock hopper.