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EXPLANATION

INTRODUCTION

The biomass for energy is obtained mainly from the industries of first and second transformation of agricultural and forestry products, residues from livestock farms, remnants of forest exploitation, crop residues and also crops implanted and exploited with The sole objective of obtaining biomass. The latter are called energy crops, but they are not forest or agricultural crops. The fundamental advantage of the crops is the predictability of their disposal and the spatial concentration of biomass, ensuring the supply.
The predictability of the availability of raw material is fundamental for any industry, and that of energy is not different.
The concentration of the resource allows a mechanized, labor-intensive and relatively inexpensive management.
This document focuses on the production of lignocellulosic biomass as raw material for the preparation of more elaborate fuels or for their direct use as a fuel, regardless of the technology applied, for conversion into usable energy. That is to say, the biomass which, once harvested or harvested from the field, is transferred with or without compaction to an industrial facility where it is transformed into a fuel of specifiable characteristics or is directly transformed into heat and / or electricity.
For the above, I will focus the present review on the cultivation of the most emerging and habitual lignocellulosic species for the production of electric energy: poplar, Populus spp. At present, most of the biomass-based power plants base their production on the operation of controlled poplars. What is targeted for this species is extrapolated to the use of forest biomass, pruning remains, and exploitations of new species such as eucalyptus, willows, Quercus, et.

HOW MUCH MICROALGAL BIOMASS CAN WE PRODUCE BY PHOTOBIORREACTORS?

Here it is convenient to make the following reflections:
1. Let's use only sunlight. We start from the fact that we are in an area with normal sunshine.
2. We will install the photobioreactors under plastic (greenhouses) to have some control over the climate and reduce maintenance.
3. We will work in 3 heights of double reactors.
4. We are going to work 330 days a year.
We used these assumptions to compare productivity per hectare under conditions similar to those of an artificially lit land cultivation.
According to the previous criteria we can produce in the order of 177 Tn / ha / year, if we work at 1.5 g / l of productivity and an annual average of 8 h of light, if we have an average of 9 to 9:30 h of light We will reach 200 Tn / ha / year.

If we compare 177 Tn / ha / year, a product (100% dry microalgal biomass) with an average calorimetry greater than 5400 Kcal, compared to 4.5 Tn / ha / year with a calorimetry of 3,400 Kcal in the case of Potato, we have a productivity 39,33 times greater with our system

IN ENERGY TERMS:

If we wanted to produce 1MWatt of electricity / day (or 41.66 kW / hr), 35,826.3 Kcal is needed, and we burn 6.63 kg of biomass (5400 KCal / kg) per hour.
To meet this requirement it is necessary to produce the same amount of biomass per hour, or 159.23 kg / day.
If we use a yield of 2 gr / liter and a daily extraction of 50% of the total volume:
We must have a productive volume of 39 807 liters of total crop.
Obviously, if the weather does not allow us to work at more than 1.0 g / l, we would need an area of ​​2,100 m2 (1/5 ha)

To produce the same amount of electricity using energy crops (forest or poplar), we would need at least:

In order to produce an amount of energy equivalent to that produced by a 1 MW plant, a crop area of ​​about 300 ha would be needed, assuming the previous average production (20000 kg ha-1) and the same type of transformation
Data source: IDAE (Institute for the Diversification and Saving of Energy), "Biomass: Energy crops", 2007.

IN CO2 IMMOBILIZATION TERMS

Carbon accumulates in the tissues of plants. In the case of trees, about 50% of the dry matter weight is carbon. We underline the term dry matter to indicate that this percentage refers to what would weigh the tree once dehydrated. The ratio of the weight of the carbon dioxide molecule to its carbon atom is 44/12 (= 3.67). Therefore, 3.67 kg of CO2 have 1 kg of carbon as an ingredient, which means that to accumulate that kg in their tissues, the plant has had to "deactivate" 3.67 kg of CO2.

In general, a ha of mature trees (a pinada, oak, etc.), can be sequestered annually up to a maximum of 5 tn of CO2, which are immobilized as "C" (mainly in the produced cell), and that as "C" only Of the order of 0.6 to 0.8 Tn / ha / year.

A production of microalgae in photobioreactors, according to our system, can immobilize in the order of 330 to 500 Tn CO2 / ha / year, which divided by 3.67 would translate into 90 - 136 Tn C / ha / year.

In general it is easy to say that a Ha of photobioreactors fixes 100 times more than a Ha of any type of forest or crop.