Things we learn from our Methane Digester, an ongoing process.

About 4 months ago we installed a Hydrogen Sulfide (H2S) seperation system on our digester.  The benefit from this is really multi-faceted, less H2S in our generators which will extend engine life, allow us to use cheaper oils to keep the engines clean, and potentially extend the oil change intervals.  Yeah, yeah I know exciting stuff.  The system is basically a air injector, that measures flow rate, and adjusts the amount of air injected into the system.  Pretty simply, well at least thats what I thought until I saw what the system cost. 

We were told not to expect to see a change for about 2 months, and to our surprise we saw nothing.  GHD, our digester company came out and reviewed the system and discovered a setting in the system was set incorrectly.  They adjusted it and this week we have discovered some things that seem to imply that it is working great. 

One of the negatives of the H2S system is that it can create some bacterial growth that tends to cling to the screens and therefore eventually plug gas flow.  This week everything seemed to running just perfect with the digester until we realized the emergency relief valve at the far end of the digester was opened, this valve is only supposed to open when the pressure gets above 8 inches of Water Column (WC).  The odd thing is the digital gas pressure guage was only showing around 2" WC. 

It was time to do some research on what was going on.  We were totally confused.  Frank eventually came up with an idea.  Just above the digester in the pipeline to the gas room is a flame arrestor, it has a radiator-like screen that prevents the very rare occasion that a spark might wander through over 100 foot of pipeline and ignite the entire digester.  Maybe this screen was growing bacteria due to the H2S system and confounding pressure guage.  He pulled the screen out cleaned it and sure enough we suddenly had over 8" WC in the digester. 

Now, our only problem is that the gas heat exchanger for genset 1 is plugged, and we are waiting for Wagner-Mienert to come clean it.  Once this is completed we strongly believe we will be running both gensets. 

Genset operations

Something to note.  The flare is only supposed to release gas if the gas pressure is above 4"WC.  Now, on the above picture notice the digester pressure is only at 3.9" WC.  But the flare is processing about 13.6 CFM of gas at a temperature of 998 degrees F.   The likely cause is that the flame arrestor needs cleaned.  The result of all this:  The H2S system appears to be working, and we clearly have enough gas to run both generators. 

Also the KWH numbers associated with each generator.  The KW numbers indicate current electrical production, and KWH is total KWH produced be each generator since we started operation over a year and a half ago.

Keep an eye out, hopefully I'll be posting our success in a few weeks.  But, the digester is a lot like a cows stomach we never really know whats going on in there.