Zhifa Sun

Energy recovery from lipid extracted, transesterified and glycerol codigested microalgae biomass

The production of methane (CH4) via the anaerobic digestion of microalgae biomass residues from the biodiesel production process has the potential to meet some of the energy requirements of the primary biomass to fuel conversion process. This paper investigates the practical CH4 yields achievable from the anaerobic conversion of the microalgae residues (as well as codigestion with glycerol) after biodiesel production using both the conventional and in situ transesterification methods. Results demonstrate that the type of lipid extraction solvent utilized in the conventional transesterification process could inhibit subsequent CH4 production. On the basis of actual CH4 production, a recoverable energy of 8.7–10.5 MJ kg−1 of dry microalgae biomass residue was obtained using the lipid extracted and transesterified microalgae samples. On codigesting the microalgae residues with glycerol, a 4–7% increase in CH4 production was observed.

Dynamic Modelling of the Wood Stack in a Wood Drying Kiln

For the design of energy efficient dryers employing heat pump systems, the dynamic response of the product to the kiln conditions must be taken into account. In this paper, the formulation of a dynamic, kiln-wide drying model is described. The model solves the unsteady-state mass, momentum and energy balance equations for both the air flow and the wood boards in drying three types of stack: normal stack, aligned stack and staggered stack. In order to represent the dynamical response of the system, the model equations provide more complete energy and mass balances than those presented in recent publications. The transient profiles of the air humidity, temperature, pressure, and velocity, and the wood temperature and moisture content along the air flow direction within the stack are obtained using this model. To illustrate the use of the model, the drying processes of sapwood boards of Pinus radiata under typical dehumidifier kiln conditions have been calculated, and the modelled results have been discussed in detail. In addition, the model has been tested by using the performance data for a commercial scale kiln. The agreement between the modelled and measured performance results shows that the model is suitable for the design and analysis of dehumidifier wood dryers.

THE INFLUENCE OF COMPRESSION WOOD ON THE DRYING CURVES OF PINUS RADIATA DRIED IN DEHUMIDIFIER CONDITIONS

ABSTRACT Measurements of drying rate of Pinus radiata at 55°C and 30% RH are presented. The data, which has been used to establish empirical models for P. radiata under dehumidifier drying conditions, was obtained in four drying runs in a drying tunnel, each yielding detailed drying curves for twelve sample sapwood boards of size 350 × 100 × 50 mm. Compression wood was found to have a significant effect on the drying rate curve, giving lower drying rates at 40–100% MC. This effect is interpreted through the use of a numerical multiple-mechanism two-zone model and quantified by using best-fit diffusion parameters from an isothermal diffusion model. A positive correlation was discovered between the moisture diffusion coefficient and initial moisture content, a strong indicator for the presence of compression wood. In the two-zone model, the compression wood effect was replicated by using a tenfold decrease in permeability to liquid flow. Attributes of compression wood that could cause reduced permeability include an increased proportion of latewood, narrower lumen, and a scarcity of bordered pits on the radial walls of longitudinal tracheids.

Optimizing efficiency and productivity of a dehumidifier batch dryer. Part 1: capacity and airflow

A whole dryer model has been used to investigate the influence of the system design on the efficiency and productivity of a batch-type dehumidifier dryer. The product is an easy-to-dry timber, Pinus radiata. The model, which has been validated at both the dryer and dehumidifier levels, includes sub-models for the whole dryer energy balance, control of preheating, temperature and relative humidity, and the airflow system. The dynamic response of the system is illustrated and the influence of the dehumidifier capacity and the kiln airflow rate on the dryer performance is established. The effect of varying the airflow system losses is also determined. On the whole, drying speed and operating income increase with the dehumidifier capacity and the kiln airflow rate. The energy used by the dryer in a complete drying cycle is strongly influenced by the fan power requirements, and the airflow system losses have a significant adverse effect on the operating income. The results demonstrate the importance of balancing the dehumidifier and the airflow system losses in order to obtain an optimum combination of drying speed and energy efficiency. Copyright

Use of dynamic modelling for the design of batch-mode dehumidifier dryers

ABSTRACT The performance of batch-mode dehumidifier dryers undergoes significant changes during the drying process due to the range of temperature and humidity conditions experienced. Consequently steady-state methods are inapplicable for determining the performance of such kilns. In this paper a dynamic dehumidifier kiln model is used to estimate the drying speed, energy use and annual income for a batch-mode dehumidifier kiln. The model has been validated at both the dryer and dehumidifier levels, and the product is Pinus radiata, an easy-to-dry plantation soft-wood. The results show that control limits for the evaporating and condensing temperatures must be well matched to maximise the drying speed in the constant rate period. In the falling rate period, it is important not to place a lower limit the relative humidity unnecessarily. The use of supplementary heat to accelerate the kiln start-up is shown to have only a small influence on the kiln performance.