Monitoring C0 2 Concentration 



Several techniques are available for monitoring C0 2 

 concentrations. All involve getting a sample of the 

 air-C0 2 mixture from the storage facility into the 

 monitoring device. A piece of flexible tubing, such as 

 1/4-inch Tygon, run just under the surface of the grain 

 in the storage facility and another small probe driven 

 deep into the grain is the most simplified form of 

 monitoring the C0 2 concentration. 



If unusually large amounts of dust and other 

 foreign material are present under the fill spout, a probe 

 should be inserted into this material because this will be 

 the hardest area to penetrate with the C0 2 gas. Deep 

 probes can be constructed of pieces of 1/4-inch 

 galvanized water pipe coupled together to achieve the 

 desired length. Flexible tubing may be used to connect 

 these deep probes with the monitor. Flexible tubing may 

 also be used as sampling probes if installed in the storage 

 facility before filling. The walls of this tubing should be 

 rigid so that they do not collapse under the pressure 

 from the grain. A tip should be placed on each proL^ 

 end to prevent entry of foreign matter. "Double-check" 

 probes (H.T. McGill Co., Houston, Tex.) may be 

 purchased for this use, or a probe tip with slits on the 

 side for gas entry may be fabricated. 



Other probes may be placed throughout the grain 

 mass to monitor the distribution and concentration of 

 the gas. However, it has been found that the gas 

 generally distributes itself evenly throughout the grain 

 mass during the later stages of the initial purge with the 

 exception of the areas having much foreign material. The 

 probe just under the surface of the grain mass is 

 important because the C0 2 concentration will usually 



start to decrease here first. This probe should not be 

 placed near the nozzle(s) of the application hose. 

 Further use of this sampling probe follows. 



Basically, three types of units can be used to 

 monitor the atmosphere in the storage facility. Also, a 

 small vacuum pump, such as the Bantam Dyna-Vac 

 model 7062 (Cole-Parmer, Chicago, III.), will be needed 

 to draw the gas sample for analysis in some of the 

 following applications. The three basic types of 

 monitoring equipment are: 



1. A Fyrite C0 2 indicator (for to 60-percent 

 C0 2 available from Fisher Scientific Co., Pittsburgh, Pa., 

 presently sells for less than $100). This may be used 

 with its own hand pump to monitor the C0 2 

 concentration from the tube just under the surface of 

 the grain. A small vacuum pump will be needed to 

 collect samples from probes placed in the grain mass. 



2. A small, portable C0 2 sampling unit with a 

 meter that reads out directly in percentage of CO in the 

 atmosphere. This unit is now under development by the 

 Gow-Mac Instrument Corp., Madison, N.J. This unit will 

 have a self-contained vacuum pump and will be battery 

 operated. The vacuum pump in this unit should be ade- 

 quate for pulling samples from probes in the grain mass. 



3. A Fisher model 25V gas partitioner or a 

 Fisher-Hamilton model 29 gas partitioner (presently at 

 $600 to $1,000). These units will also analyze for 

 oxygen and nitrogen in the sample. Other equipment 

 necessary to place this equipment in operation will cost 

 several hundred dolors. Therefore, this system should 

 only be considered by applicators who plan to run a 

 large number of gas samples and wish to obtain a high 

 degree of accuracy. 



STORAGE FACILITY PREPARATION 



Sealing 



All areas where C0 2 might escape on all types of 

 storage facilities, such as fill spouts, emptying chutes, 

 and manholes, should be sealed with duct tape 

 (obtainable from refrigeration or air-conditioning supply 

 houses) before introducing the C0 2 . Similarly, 

 cross-aeration ducts in concrete silos should be sealed 

 with taped-on polyethylene film or plywood. This may 

 necessitate turning enough grain so that access may be 

 gained. The cap on round or square metal bins should be 

 sealed with duct tape or caulking compound before 

 applying C0 2 . 



Application of this gas creates a positive pressure in 

 a storage facility that must be relieved (discussed below). 

 If the facility is equipped with an aeration duct or a fan, 

 or both, this is a good place to relieve the pressure. After 

 the initial purging, when the concentration is reached, 

 this area should be sealed off. 



Installation of C0 2 Input Hose 

 Into Storage Facility 



A piece of plywood cut to fit any convenient access 

 area can be drilled to allow the input hose to be inserted 

 into the headspace. The hose should be attached to a 

 structural cross member, if present, so that the C0 2 is 

 delivered onto the grain mass. The hose should be 

 supported in a semirigid manner in other types of 

 storage facilities. The hose nozzle should be at least 3 

 feet above the grain surface. It is desirable to "T" off of 

 the host nozzle with two short pieces of hose, so that 

 better distribution of the gas can be obtained over and 

 down into the grain. "T's" can be obtained at most 

 garden supply outlets. 



The gas sampling lines can be accommodated by 

 holes drilled in the piece of plywood cut to fit an access 

 port in the headspace. This piece of plywood should be 

 taped to the top of the port with duct tape. 



