This paper is concerned with numerical methods for a finite difference
system of reaction-diffusion-convection equation under nonlinear boun
dary condition. Various monotone iterative methods are presented, and
each of these methods leads to an existence-comparison theorem as well
as a computational algorithm for numerical solutions. The monotone pr
operty of the iterations gives improved upper and lower bounds of the
solution in each iteration, and the rate of convergence of the iterati
ons is either quadratic or nearly quadratic depending on the property
of the nonlinear function. Application is given to a model problem fro
m chemical engineering, and some numerical results, including a test p
roblem with known analytical solution, are presented to illustrate the
various rates of convergence of the iterations.