Critical Engineering Considerations In A CBG/BioCNG Plant

<p>If everyone talks about economics, someone needs to talk about engineering. It is part of our responsibility being a technology provider for CBG/BioCNG Plants.</p><p>A quick list of critical engineering parameters related to Biogas. BioCNG, Compressed Biogas plant. This article has nothing about economics.</p><p><strong>Raw Material</strong></p><p>The raw material, the mix, the solids in it, proteins and carbohydrate in it, dry weight, cellulose, lignin, oil content - decides the size of a digester. This makes every plant different by itself. Some rule of thumbs work, which all of us tend to make it look simple. Using gravity to our advantage is also a prime consideration.</p><p><strong>Layout</strong></p><p>Layout eats away space, makes pipelines longer, strains workmen unnecessarily. A good and logical flow of the process, no criss-cross, enough space for the vehicle movements, storage spaces, buffer spaces per the safety norms, and blending the layout with existing buildings in case of an industrial captive plant is a key thing to keep in mind. A bad layout would look like patched jeans.</p><p><strong>Piping</strong></p><p>Gas has an abrasion value too. Too fast will erode the thickness of the piping, creating noise and vibrations. Every bend in the pipeline drops the efficiency of movement. There can be a hammer effect everywhere. Equipment comes at a certain size. The hungry equipment needs buffers than a slow mover. If the entire line is not balanced we will end up with wrong velocity, pressure drop and erosion of pipes.</p><p><strong>Equipment Selection</strong></p><p>We are often spoiled by the choice. The Engineer's choice may not suit the accountant&rsquo;s choice though. The key is line balancing if we take the quality and efficiency of equipment as granted. The major challenge we would come across is equipment available for 500m3/h but the flow is 487m3/h. This is where line balancing plays a role.</p><p><strong>Pressure</strong></p><p>Across the end-to-end flow there will be low pressure requirements, high pressure requirements, Gas temperature changes. At digester level we are at atmospheric pressure, it goes through various levels and finally needs to reach 200-250bar to get into the cylinders. Once pressure is raised, reducing it makes no sense at all. Have I already said atmospheric pressure changes from place to place?</p><p><strong>Composition of Gas</strong></p><p>As the input varies, temperature varies, bacterial multiplication varies, pH of the digestate varies.... the composition of the raw biogas varies too. Whole of the engineering calculations shall accommodate a range of composition and not a fixed one value. As we remove H2S, Moistures, Carbon Dioxide, Ambient temperature changes the Volume, flow, and pressure changes. Most are calculations and many are experienced based assumptions too.</p><p>If well care is taken, we are near success as engineers, rest is left for the microbiologists.</p><p>&nbsp;</p>
KR Expert - Shashi Hegde