The following is an excerpt from The Morning News, Wilmington, Delaware (August 3, 1977): “Investigators sift through the debris from blast in quest for the cause [that destroyed the new nitrous oxide plant]. A company spokesman said it appears more likely that the [fatal] blast was caused by another gas—ammonium nitrate—used to produce nitrous oxide.” An 83% (wt) ammonium nitrate and 17% water solution is fed at 200°F to the CSTR operated at a temperature of about 510°F. Molten ammonium nitrate decomposes directly to produce gaseous nitrous oxide and steam. It is believed that pressure fluctuations were observed in the system and, as a result, the molten ammonium nitrate feed to the reactor may have been shut off approximately 4 min prior to the explosion. Assume that at the time the feed to the CSTR stopped, there was 500 lbm of ammonium nitrate in the reactor. The conversion in the reactor is believed to be virtually complete at about 99.99%.
Additional information (approximate but close to the real case):
ΔHRx∘=−336 Btu/lbm ammonium nitrate at 500∘F (constant)CP=0.38 Btu/lbm ammonium nitrate⋅∘FCP=0.47 Btu/lbm of steam⋅∘F−rAV=kCAV=kMVV=kM(lbm/h) where M is the mass of ammonium nitrate in the CSTR (lbm) and k is given by the relationship below.
T (°F) 510 560
k (h-1) 0.307 2.912
The enthalpies of water and steam are Hw(200∘F)=168 Btu/lbmHg(500∘F)=1202 Btu/lbm
(a) Can you explain the cause of the blast? Hint: See Problem P13-3B.
(b) If the feed rate to the reactor just before shutoff was 310 lbm of solution per hour, what was the exact temperature in the reactor just prior to shutdown? Hint: Plot Qr and Qg as a function of temperature on the same plot.