Session: K6-08: HEAT TRANSFER IN ENERGY SYSTEMS - WASTE HEAT I

Paper Number: 122016

122016 - Powering a TLUD Biomass Pyrolyzer Using its Own Waste Heat and Thermoelectric Devices 

Abstract: 

It has become evident that the impacts of climate change are increasing in severity and frequency.  Longer drought periods, year-long wildfire seasons, rising sea levels, and catastrophic flooding, among others, have devastated communities around the world.  Prompt introduction of greenhouse gas (GHG) emission reduction policy is critical to reverse the course of climate change, however, utilization of waste heat has also been identified as an effective way to meet climate change mitigation targets.  Biomass from the forest or agricultural sector can be an important source of methane emissions if it is left to decay, or it can generate a variety of pollutants and particulate matter if it is burned in open piles or in wildfires.  Due to this, in California, the San Joaquin Valley Air Pollution Control District is banning open burning of biomass starting in January of 2025. 

On the other hand, biomass can be part of the climate change solution when it is used in thermochemical processes such as pyrolysis or gasification to produce electric power or industrial heat without adding carbon to the atmosphere and providing a stable form of carbon sequestration in the form of biochar.  The traditional model of biomass processing relies on centralized plants where biomass transportation can be an important source of greenhouse gas emissions.  Therefore, mobile units that can process the material at the biomass source are gaining interest.  A simple pyrolyzer that is inexpensive to build and easy to operate is the Top-Lit Up-Draft (TLUD) design.  This reactor utilizes a limited amount of air flowing upwards to provide partial oxidation of the biomass, converting it to biochar.  The unit can operate in natural convection mode, producing the updraft flow of primary air based on the temperature difference between the reactor and the ambient air.  A source of secondary air is usually utilized to burn the pyrolysis gas that is produced in the reactor.  However, this configuration produces biochar of inconsistent quality that makes it difficult to utilize in soil-amendment or industrial applications.  A small electric fan can be used to stabilize the air flow rate, but this means that a source of electricity should be available, such as a battery or generator that can be brought to remote locations. 

Thermoelectric devices have been gaining interest since improved materials have increased electric-generation efficiency and the temperature difference that these devices can handle.  This paper explores the use of high-temperature thermoelectric generator modules to take advantage of the waste heat generated at the stack of the TLUD pyrolyzer.  The electric power generated is used to power the primary-air fan, eliminating the need for an external source of electric power available at remote locations.  The heat transfer analysis to maintain the thermoelectric module operating within its recommended temperature range is provided and biochar properties such as surface area and pore volume are obtained at different heights of the TLUD pyrolyzer to analyze the consistency of the biochar produced.   

Presenting Author: Ziad Nasef Univ. of California Merced

Presenting Author Biography: Ziad Nasef is a Graduate Student and PhD candidate at the Department of Mechanical Engineering at the University of California at Merced. His work focuses on the pyrolysis of biomass and the improvement of the consistency of its properties as the process is scaled up.

Authors:

Ziad Nasef Univ. of California Merced
Nathan Nugen Univ. of California Merced
Edbertho Leal-Quiros Univ. of California Merced
Gerardo Diaz Univ Of California Merced