Design of a Process Control System for Combustion Regulation by Moisture Content Measurement in Biomass Feed

Abstract

Biomass has the capacity to generate a major part of the global renewable energy demands due to its large supply, versatility, and readily exploitable nature. Biomass can be produced from natural sources like wood waste, grasses, trees, and fast-growing energy crops. Biomass wood chips are produced from crushed trees and can be fed into combustion systems to supply heat energy to buildings. However, depending on the type of trees, season of harvest and storage conditions of biomass wood chips the moisture content in the biomass wood chips may vary. The variation in moisture content of biomass wood chips is a major quality issue for large district heating systems because it has negative impacts on the overall system efficiency and heat exchange effectiveness. Notwithstanding, just a few research works have been done in this field. This research fills the knowledge gap by providing an overview of biomass combustion systems and moisture measuring techniques that are available in literature. It further builds on the existing literature by using SIPOC (suppliers, inputs, process, outputs, customers) process map and proportional-integral-derivative (PID) control loop to discuss the effects of varying moisture content on the biomass combustion system. The research presents the design of a process control system for combustion regulation using the measured moisture percentage in biomass wood chips. The control system was designed using Lean Six Sigma tools and the seven major building blocks of the control system design process. The microwave moisture sensor was selected as the most suitable sensor for the process control and technical solutions for its installation were discussed. Experiments were also performed for process control and improvement, and they provide a basis for future research.