Juha Anttila

Sustainable pulp production from agricultural waste

This paper introduces a new type of chemical pulping process technology. In the design of the process, significant efforts have been made to attain sustainable utilisation of natural resources. The paper discusses the essential issues to be taken into consideration when annual fibres are used in the pulp and paper industry. The paper focuses on the physical and chemical properties of the raw materials and their relationship with the environmentally friendly concept of cellulose and paper production. The chemistry and structure of the Chempolis process as well as certain properties relevant to pulp and paper qualities are described. The concept of the Chempolis process is based on three major stages: delignification, bleaching and recovery of acids. In acidic delignification conditions, the dissolution of silicon present in the raw material is prevented, while the nutrients are dissolved. Furthermore, the hydrolysis of xylan can be controlled. To minimise the cost of recovery, cooking chemicals are selected from the compounds which are formed during the processing of lignocellulosic. Alkaline TCF conditions are used in bleaching to enable totally effluent-free operation. The Chempolis process is based on a closed system. Apart from the bleached chemical pulp, the output flows include solid organic biofuel, which can be used to generate energy for the mill and fertilizer for the cultivation of raw material. Due to the simplicity of the process and the efficient raw material utilisation, the mill economy is attractive.

The boundary element spline collocation for nonuniform meshes on the torus

The spline collocation method for a class of biperiodic strongly elliptic pseudodifferential operators is considered. As trial functions tensor products of odd degree splines are used and the collocation is imposed at the nodal points of the tensor product mesh. It is shown that the collocation problem is uniquely solvable if the maximum mesh length is small enough. Moreover, the approximation is stable and quasioptimal with respect to a norm depending on the order of the operator and the degree of approximating splines. Some convergence results are given for general and quasiuniform meshes. The results cover for example the single layer and the hypersingular operators.

A spline collocation method for parabolic pseudodifferential equations

The purpose of this paper is to examine a boundary element collocation method for some parabolic pseudodifferential equations. The basic model problem for our investigation is the two-dimensional heat conduction problem with vanishing initial condition and a given Neumann or Dirichlet type boundary condition. Certain choices of the representation formula for the heat potential yield boundary integral equations of the first kind, namely the single layer and the hypersingular heat operator equations. Both of these operators, in particular, are covered by the class of parabolic pseudodifferential operators under consideration. Moreover, the spatial domain is allowed to have a general smooth boundary curve. As trial functions the tensor products of the smoothest spline functions of odd degree (space) and continuous piecewise linear splines (time) are used. Stability and convergence of the method is proved in some appropriate anisotropic Sobolev spaces.