Sorbent injection system

In a furnace (10) in which a sulfur-bearing fuel is burned, a sorbent material such as limestone is introduced into the upper portion of the furnace through a plurality of nozzle arrangements (40). Each nozzle arrangement comprises a pair of concentric pipes (42,44) with deflector means (46) located between the pipes and adjustable by means (54), so that the sorbent material introduced through the outer pipe is dispersed in an area near the furnace wall, while that introduced through the inner pipe is projected to the central portion of the furnace. There are sufficient nozzle arrangements, and they are so located, so as to cover substantially the entire cross-sectional area of the furnace with sorbent material.

BACKGROUND OF THE INVENTION 
In recent times, coal has become a viable fuel for generating steam. Some 
coals include a high percent of sulfur, which will be released to the 
atmosphere in the form of hydrogen sulfide or sulfur oxide unless steps 
are taken to prevent this release. One means of preventing this SO.sub.x 
release to the atmoshpere which is presently being used is to add a 
sorbent, such as limestone, to the furnace, so that the sulfur combines 
with the calcium and magnesium to form solid sulfates. There are problems 
associated with this solution. The limestone must be added at the proper 
location in the furnace so that the limestone is not deadburned. Also, the 
limestone must be dispersed throughout the combustion gases such that it 
will come into intimate contact with and react with most of the sulfur 
compounds, an stay in contact for an extensive period of time, at the 
proper temperature (1700.degree.-2200.degree. F.), so that much of the 
sulfur will combine with the calcium and magnesium to form sulfates. To 
compound the problem of good distribution of the sorbent throughout the 
gas flow, if the load on the steam generator changes, and the firing of 
the furnace is thus varied, the flow pattern of the combustion gases can 
change. 
SUMMARY OF THE INVENTION 
In accordance with the invention, sorbent, such as limestone, is introduced 
into the upper portion of the furnace through a plurality of concentric 
pipes. An adjustable member located in the annular space between the pipes 
permits the amount of, and flow characteristics of, the air-borne sorbent 
being introduced into the furnace. Thus, the concentric pipe arrangements 
can be adjusted to get the proper sorbent introduction to disperse it 
fairly evenly throughout the combustion gas flow. Other suitable gas, such 
as recycled flue gas, can be used instead of air to transport the sorbent.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Looking now to FIG. 1, numeral 10 denotes a coal fired furnace, having a 
plurality of levels of burners 12 therein with each level having a burner 
mounted in each of the four corners thereof. Air is supplied to the 
burners from fan 16 through ducts 18 and 20. Air is also supplied to 
pulverizer 22 through duct 24. Pulverized coal having a sulfur content is 
transported to the burners in an air stream through ducts 26 and 28. There 
are separate air and fuel ducts leading to each individual burner, with 
separate valves and controls (not shown) also, so that each burner can be 
independently controlled. The combustion gases swirling upwardly into the 
furnace give up heat to the fluid passing through the tubes 30 lining all 
four of the furnace walls before exiting the furance through horizontal 
pass 32, leading to the rear pass 34. Both the furnace and the rear pass 
contain other heat exchange surface (not shown), for generating and 
superheating steam, as is well known in the art. 
Located in the upper portion of the furnace are a plurality of nozzle 
arrangements 40, through which a sorbent material, such as limestone, can 
be introduced. The sorbent is conveyed in a stream of air or other gas, 
and introduced in such a manner that it intimately contacts as much of the 
combustion gases as possible, so that the magnesium and calcium can react 
with the sulfur in the gas to form sulfates. To accomplish this, it is 
desirable to introduce the sorbent in such a manner that it substantially 
covers the entire cross sectional area of the furnace. 
Looking now to FIGS. 2 and 3, the location of, and construction of, the 
nozzle arrangements 40 are shown in more detail as to how they accomplish 
the desired sorbent dispersion across the entire cross-section of the 
furnace 10. As can be seen in FIG. 2, each nozzle arrangement 40 consists 
of a pair of concentric pipes 42 and 44. Attached to and located near the 
outlet end of the inner pipe 42 is an annular frusto-conical deflector 46. 
This deflector causes the sorbent flowing in annular passage 50 to be 
discharged into the furnace in a dispersed manner close to the furnace 
wall. The high penetration flow through the inner pipe 42 is projected 
straight into the furnace, and will carry to the central portion thereof. 
FIG. 3 illustrates how a number of the nozzle arrangements 40 positioned in 
the front and rear walls can be used to introduce sorbent in such a manner 
so as to completely cover the cross-sectional area of the furnace. The 
inner pipe 42 can be moved longitudinally, so that the deflector is 
positioned closer or further from the end 52 of the outer pipe 44, if 
desired, by manipulation of handle 54 (FIG. 2). Radial bars or rods 56 
secured to the inner pipe 42 keep the pipes concentric during such 
movement. This adjustment permits more or less sorbent to be introduced 
close to the furnace wall, depending on the firing rate of the furnace. 
This adjustment also permits the initial introduction setting so as to 
assure complete coverage of the entire cross-sectional area of the furnace 
with sorbent. Each of the nozzle assemblies can be individually adjusted.