[Digestion] flex-use biogas plant?

[Bjorn Dahlroth]

Hello everyone
This is more a qquestion of which segment(s) of the energy market that you will find most profitable to work on and that varies a lot - not only between countries but also from one city or one farm to another. Prices on the energy market are different in different places and so are the investment and operation costs for reaching the clients. The market in many places in Europe is partly strictly commercial partly political.

You can use the gas directly for heating or for production of electricity or combined heat and power in special gas engines that are suitable for gas with medium enery content or you can upgrade it to almost natural gas quality and pipe into the natural gas system or compress it further to use as fuel for cars or city buses. You will find this kind of applications here there and it is quite ordinary reasonably well developed commercial technology. In Sweden we have I believe all kinds of these applications for land fill gas and for gas from digesting plants. From the gas users point of view there is no differensce between these sources - you by energy and you pay. Some of these applications are commecial - especialyy when it comes to using land fill gas - some are what we call demonstration plants.

What is not so well developed yet - as I see it - is to achieve the highest conversion efficiency from mixed biodegradable matter and in cases where the mixture is not constant in time but variable, just as the situation is when you want to work with various kinds of waste, and this is normally the case when we are talking of larger plants for food industries or for municipal use. Even in small scale farm digestion it is usually question of a kind of waste that that you want to use I an different and hopefully smarter and economical way. If put the manure directly on the field or even if you composte it first you loose very much of the bioenergy content and quite a lot of the nitrogen content goes up the air. 

If you have pure sugar, pure cellulose or pure animal fat it is not difficult to achieve a high conversion efficiency but if you mix it and want a high gas yield in a short through-put-time it is a different story. To handle the impurities and the variations and the inhomogenity in mixtures and make the variouis kinds of bacteria thrive and cooperate rather then disturbing each other,that is the challenge. To handle impurities can be done with manual separation, sorting, screening, storaging, mixing, mashing, milling - you name name it - but all these things cost money and give you operational problems. It is the same in both small and large scale plants and it is epecially in this field that this kind of Internet network is very valuable as a means of exchanging information.

Bjorn Dahlroth

 
-----Ursprungligt meddelande-----
Från: digestion-bounces at listserv.repp.org [mailto:digestion-bounces at listserv.repp.org] För Jason Perry
Skickat: Thursday, November 16, 2006 12:48 PM
Till: digestion at listserv.repp.org
Ämne: [Digestion] flex-use biogas plant?

Hi all,

This is more of a question about energy recovery from biogas than about 
digestion itself. This is also a semi-hypothetical situation. Let's say 
you have a school in New York State that has multiple dairy farms within 
3 miles. Peak natural gas use for heating the school is in 
January/February; gas use drops to almost nothing in the summer. In 
theory, if all of the dairy manure were recovered and brought to a 
central digester near the school, the biogas produced could more than 
cover the peak heating demand.

But what to do with surplus biogas for the rest of the year? Generate 
net-metered electricity, of course.

Does such a system exist, where biogas is diverted from one energy use 
to another (or some combination in between) depending on need?

Thanks for any thoughts,

Jason

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