Ralf Pecenka

Harvesters for short rotation coppice: current status and new solutions

Mechanization in the harvesting of short rotation coppice on farmed land is a prerequisite for the expansion of short rotation coppice cropping. Existing harvest lines can be classified as log, bundle, bale, or chip lines; the latter are widely considered the most economical. Despite the development of more than 20 different harvesting machines and assemblies for chip lines in the past decade alone, only a few have progressed beyond the prototype stage. In addition to special mower tools already available for conventional forage harvesters, there is a great need for low-cost tractor-mounted chip harvesters. Therefore, a novel working principle for a mower-chipper was developed and tested. In contrast to most other solutions, the trees remain in an upright position while mowing and chipping. The harvest machine has a compact single rotor bearing a circular saw blade with a diameter of approximately 1000 mm. Knives arranged radially are attached to the saw and offset above the disk with spacer blocks. To ensure even feeding of the mower-chipper unit, numerous passive and active machine elements were tested to find a reliable solution for practical application. With the investigated harvester, trees with stem diameters up to 15 cm and 10 m in height could be successfully harvested at very promising working speeds of 3–5 km/h. The Class P45 wood chips produced satisfied the CEN/TS 14961:2005 standard.

Fibre boards and composites from wet preserved hemp

It is absolutely necessary to reduce plant investments and processing costs in order to make natural fibres more attractive for farmers and industry. Conventional hemp fibre production is based on field drying and straw retting – connected with a high weather risk. Therefore, a novel weather-independent technique has been developed. Hemp is harvested by means of a chopper followed by anaerobic storage. A pilot plant with a processing capacity of 300 kg h −1 (dm) fibre material has been built up and tested. The whole plant material can be processed to products like insulation materials, fibre boards or granulate for injection moulding.

Wet Processing of Hemp: An Overview

Normally, the production of fibers from agricultural fiber crops is based on field drying and retting of plant straw. As weather conditions at the usual harvest time are often problematical for harvesting and retting, the development of weather-independent supply chain technologies is very important. The weather risk can be avoided, if, e.g., hemp after being harvested with a conventional forage harvester is directly processed to final products, or stored by wet preservation. Furthermore advantageous is that the whole plant material without any loss is processed to final products like fiber boards, insulation materials, or fibrous materials for natural fiber reinforced composites. Especially for this purpose a pilot plant has been built up and is tested till present. The investigations have shown that conventional technologies of ensiling are capable for the preservation of hemp for more than one year.

Storage Problems of Poplar Chips from Short Rotation Plantations with Special Emphasis on Fungal Development

Abstract - There are several problems in storing wood chips freshly harvested from short rotation plantations, which result in quality losses as well as in dry matter and energy losses. The factors influencing the degradation of raw material are examined in this paper with special focus on fungal development. An excessive growth of fungi is connected to dry matter losses and also to an increased health risk during raw material handling. The following factors were measured during 6 months storage of poplar wood chips depending on particle size: box temperature, moisture content, pH-value, appearance of fungi in the storage and the concentration of fungal particles in the air. The results show a close connection between particle size, temperature and attack of fungi. During the storage mesophilic and termophilic species of the genera Alternaria, Aspergillus, Cladosporium, Mucor and Penicillium appeared. The concentration of fungal particles is the highest for fine chips and decreases in bigger particles. There was a special focus on the investigation of the properties of coarse chips (G 50), which represent a good compromise between handling, storage losses and health risk due to fungal development. Kivonat - Rövid vágásfordulójú nyár apríték tárolási problémái, különös tekintettel a kifejlődő gombákra. Frissen kitermelt rövid vágásfordulójú fafajokból előállított apríték tárolása során számos probléma merül fel, melyek eredménye minőség-, szárazanyag- és energiaveszteség. Ebben a tanulmányban a nyersanyag-degradációt befolyásoló tényezők kerültek vizsgálatra, különös tekintettel a kifejlődő gombákra. Ezek rendkívüli elszaporodásának köszönhető a szárazanyag-veszteség mellett a nyersanyag kezelése során fellépő, megnövekedett egészségügyi kockázat is. Nyár faapríték hat hónapos tárolása folyamán az aprítékméret függvényében a következő tényezők mérése zajlott: a tárolón belüli hőmérséklet, nedvességtartalom, pH, a tárolóban megjelenő gombák és azok száma a levegőben. Az eredmények szoros összefüggést mutatnak, különösen az aprítékméret, a hőmérséklet és a gombák száma közt. A tárolás során mezofil és termofil gombák fejlődtek. A következő nemzetségekhez tartozó fajok voltak megfigyelhetők: Alternaria, Aspergillus, Cladosporium, Mucor, Penicillium. A gombák száma a finom aprítéknál volt a legmagasabb, ami az aprítékméret növekedésével csökkent. A kutatás folyamán különös szerepet kapott a középfinom apríték tulajdonságainak vizsgálata (G 50), mely kompromisszumos megoldást jelent a kezelés, tárolási veszteségek és a kifejlődő gombáknak köszönhető egészségügyi kockázatok között.

Process-Technological Evaluation of Harvesting Hemp in Winter

The objective of the project was the evaluation of potential possibilities of hemp harvest in the winter for Germany, considered its average climate conditions. Prerequisite for a harvest is that hemp straw achieves low moisture content suitable for storage. For this purpose, hemp stalks were sampled regularly from a hemp field in Potsdam (Germany) between January 2010 and March 2011 to determine their dry matter (DM) content. By the end of February, the hemp stalks achieved a dry matter content of 90%. To obtain information about the weather-related hemp straw moisture sorption isotherms of hemp stalks were determined in a climate chamber, and the change of material moisture of the stalks was measured under changing humidity levels. Based on the findings, an algorithm for estimating available harvesting times for several years was developed. Results show that significant harvesting times may be achieved in the months of February and March.

Design of Competitive Processing Plants for Hemp Fibre Production

Despite an annually growing demand for natural fibres accompanied by worldwide increasing fibre prices as well as long tradition and experience in fibre processing, the production facilities for hemp and flax fibres are very limited in Europe. At present, the lack of modern harvesting and economic processing technologies seem to be the greatest obstacles for hemp fibre producers under the changing conditions of international raw material markets. Therefore, detailed investigations of all process stages of hemp fibre processing have been carried out at the Leibniz Institute for Agricultural Engineering (ATB). A novel hemp processing line has been developed, installed, and tested at industrial scale in the last 3 years. Investigations regarding optimum plant layout have shown that a straw throughput of approximately 4 t h−1 is required for economic fibre production for all new processing lines at currently high straw prices of more than 150 € t−1. Throughputs in the range from 4 to 6 t h−1 showed a favourable relation between profit and investment cost. At throughputs higher than 6 t h−1, the profit per ton processed straw can be further increased. But investment and straw logistic cost increase at these high-throughput levels often much faster.

Effect of densification variables on density of corn cob briquettes produced using a uniaxial compaction biomass briquetting press

ABSTRACT Densification of loose biomass improves its properties for use as fuels. To design efficient briquetting equipment, there is a need to study properties of briquettes under different conditions. In this study, the effects of process variables (pressure, temperature, and hold time) and a material variable (particle size) on the density of corn cob briquettes were investigated. It was discovered that increasing the pressure, temperature, and particle size had positive effects on the density of biomass briquettes. The density of biomass briquettes produced using the selected values of pressure (9, 12, and 15 MPa), temperature (90°C and 120°C), hold time (7.5 and 15 min), and particle size (<2.5 mm and >2.5 mm) ranged between 570 and 1300 kg/m3.