Two-stage agglomeration of fine-grained herbal nettle waste

Abstract

A b s t r a c t. This paper compares the densification work necessary for the pressure agglomeration of fine-grained dusty nettle waste, with the densification work involved in two-stage agglomeration of the same material. In the first stage, the material was pre-densified through coating with a binder material in the form of a 5% potato starch solution, and then subjected to pressure agglomeration. A number of tests were conducted to determine the effect of the moisture content in the nettle waste (15, 18 and 21%), as well as the process temperature (50, 70, 90 o C) on the values of densification work and the density of the obtained pellets. For pre-densified pellets from a mixture of nettle waste and a starch solution, the conducted tests determined the effect of pellet particle size (1, 2, and 3 mm) and the process temperature (50, 70, 90 o C) on the same values. On the basis of the tests, we concluded that the introduction of a binder material and the use of two-stage agglomeration in nettle waste densification resulted in increased densification work (as compared to the densification of nettle waste alone) and increased pellet density.K e y w o r d s : agglomeration, nettle waste, binder, starch INTRODUCTIONOne of the types of post-production waste produced in herbal companies is the nettle waste obtained during herb processing. The amount of waste left over from the process of herbal production is relatively large, with its utilisation being problematic due to the very small particle sizes of waste fractions.In the case of Herbapol Białystok S.A., the annual production of herbal (usually nettle) waste, amounting to approx. 30 t, is usually sold cheaply or given away for a refund of the transport price.The most common method of herbal waste management is using herbal waste as a fodder additive. Depending on the species of the plant used, herbs exhibit bactericidal (e.g. sage), immunostimulating (Echinacea), antioxidant (e.g. rosemary), sedative, and soporific (e.g. melissa) properties. They can also lower cholesterol levels in the body. In addition, some of these improve the aroma and flavour of fodder. In order to take advantage of this range of properties, mixtures of different plants are often used (Hanczakowska, 2007). The effect of herbal additives in pig fodder on nutritional results is presented in a paper by Paschma (2004), among other studies.One of the methods of plant biomass waste management, including fine-grained herbal waste, is its pelleting or briquetting into a solid fuel (pellets, briquettes), and then using the resulting product as fodder or fuel (subjecting it to combustion). Various kinds of post-production plant waste have been densified into the form of pellets or briquettes: olive tree pruning residues (Carone, 2010), cork powder waste (Montero et al., 2014), blends of poplar and pine sawdust (Monedero et al., 2015), corn stover and switchgrass (Mani et al. 2006a(Mani et al. , 2006b, rice straw and rice bran (Chou et al., 2009), herbaceous crops (Gilbert et al., 2009, mixtures...

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