Optimal processing of greenhouse crop residues to use as energy and CO2 sources

Abstract

This work presents the development of suitable strategies focusing on greenhouse crop residues as energy and CO 2 sources for improved food production in greenhouses. The utilization of greenhouse crop residues in combustion processes for heating and carbonic enrichment in greenhouses has previously been developed and evaluated. Nevertheless, greenhouse crop residues present several problems that make it difficult to use them for these purposes. Among the characteristics that can impede their use are excessive moisture and ash contents as well as their low density. In this work, the relevant solid fuel properties for this type of biomass have been studied. In addition, three pre-treatment strategies are proposed and evaluated, which aim to enhance the fuel quality of this biomass. These strategies were: 1) first relates to the drying strategy employed for reducing greenhouse crop residue moisture. 2) the second one relates to a reduction in ash content by avoiding contact with greenhouse soil and 3) mixing with other biomass kinds with better quality as solid fuels. The assays performed showed that these strategies were successful, resulting in biomass with a high heating value, up to 26.9 MJ/kg, and a lower ash content than untreated residues, with values as low as 13.0% dry weight. This value is closer to that for the standard biomass most commonly employed in direct combustion applications. The biomass produced has been verified as suitable for conventional boilers with thermal efficiencies up to 70%. The methods developed allow to reuse greenhouse crop residues as greenhouse fuel, providing both heat and CO 2 ; thus enhancing production and sustainability.

Boiler Combustion Optimization of Vegetal Crop Residues from Greenhouses

“…The only part discarded was the roots. Discarding the roots significantly decreases the ash content (as demonstrated in previous research) [15]. The plants were laid out to dry for about two weeks in the same greenhouse in which they were grown.…”

“…Four different biomass types were studied in this work: Olive pits, pine pellets, tomato-crop biomass, and a blend of the latter with almond prunings (75-25%). In a previous work, several characteristics were determined to study their appropriateness for use in direct combustion applications [15]. These characteristics were the water and ash content, and the calorific value.…”

“…This material has a higher adsorption capacity for CO 2 than for toxic gasses, increasing with pressure and decreasing with temperature. The working operational conditions were set to 2 × 10 5 Pa and a maximum temperature of 40 • C. The system used is also described in References [15,33,35]. The levels present in the gas stream coming from the tank were measured on their way to the CO 2 enrichment process in the greenhouse (once the capture process was completed).…”

Valorization of Greenhouse Horticulture Waste from a Biorefinery Perspective

“…A small proportion, especially discarded fruits, can be used for livestock feeding as well. In contrast, the use of these waste products as raw material for the production of biofuels and/or bio-based products in biorefinery plants is nowadays seen as an interesting scenario for the sustainable valorization of these residues [ 14 ].…”

Natural Organic Compounds for Application in Organic Farming

“…According to the World Health Organization (WHO), agrochemicals can be classified according to their toxicity depending on the median lethal dose (LD 50 ) for rats (Table 1) [2]. An improvement to this practice corresponds to the use of this biomass to generate energy in a sustainable way [24,25]. Moreover, the incorporation of these residues, as green manure, can provide nitrogen to the soil, through biological nitrogen fixation, increasing the supply of N to subsequent crops, allowing the reduction of chemical fertilizer applications [26,27].…”