Two key world problems, waste disposal and economical electrical generation, can be solved simultaneously through a clean and economical waste-to-energy facility.
The commercial waste industry includes all those who collect waste from the simplest “collect waster and transport to a landfill” to the more complex “collect waste and process into re-usable components and energy”. This article will cover how we can collect material and fuel a clean energy system for our future, while saving clean water and air.
Why Use Biomass? Biomass refers to living and recently dead biological material—such as green, wood, biodegradables and municipal solid waste (MSW)—that can be used as fuel to generate energy. Today, many States require 20 percent of generated power to be from renewable sources. Therefore, biomass is beneficial because most times it is the low-cost available fuel and can allow municipalities to provide heat and energy to nearby industrial/commercial users and their own facilities. Many biomass facilities can be tailored to the fuel stocks readily available in your region. Because multiple types of fuels can be used to produce energy, revenue sources from biomass can include tipping fees, electrical generation and recycling.
Types of Biomass Systems There are four types of biomass systems, including gasification (plasma technology and gasification from combustion process), incineration, solid fuel boilers and rotary cascading bed combustion (RCBC).
Gasification is a multi-step process using high-temperatures to convert biomass into a gas mixture that can be used for energy (see Figure 1). It is great for feedstock and product flexibility, emitting low emissions with high efficiency and it has energy security.
However, gasification is a complex multi-stage process with two-stage emissions control and an expensive initial setup because it includes several primary systems which are each complex in their own right:
A gasification chamber with combustion cleaning
Gas-air mix control and storage under pressure
Gas combustion and heat use
With its accompanying multiple of components plus a pressurization system and pressurized containers, gasification is more costly, by multiples, than the simpler direct conversion Rotary Cascading Bed Combustion system. In addition, up-front feedstock processing and pressurization is required as well as purifying the syngas (gas made synthetically rather than the natural variety). Finally, there is loss of BTU to ash and char.
A component of gasification is plasma, which uses high voltage arcs to break down waste in elemental gas and solid waste, resulting in syngas that can be used as fuel (see Figure 2). Although it is a complex, multi-stage process, requires high maintenance and is a very expensive technology, plasma gasification does allow for recycling of large quantities of MSW and exceptionally high temperatures achievable.
The process of simply burning all materials to produce energy, incineration is an inexpensive volume reduction, simpler than gasification and is used quite regularly in the commercial waste industry (see Figure 3). However, incineration does result in the loss of all useful recyclable material, a lack of consistency in material burning, emissions problems and needs extensive permitting.
Solid Fuel Boiler Systems
These types of systems are typically coal fired boilers, including stoker grate, fluidized bed, mass burn and pulverized firing with suspension burn of the biomass (see Figure 4). With high reliability with good care, existing facilities can be used for these systems. Usually designed for a specific fuel, flexibility may be more difficult to achieve and there are few vendors that offer smaller size units because it is generally expensive to construct new systems.
Rotary Cascading Bed Combustion
Using mechanical principles to combust waste and biomass at lower temperatures through longer burn cycles (resulting in lower emissions), rotary cascading bed combustion is a mechanical process that allows for a more complete burn (see Figure 5). It has fuel flexibility (the computer will automatically mix various types) and size adaptability as well as simple fuel feed and ash handling systems. Although these types of systems may require a support fuel for very wet materials and operational experience is limited, the cost is significantly lower than other biomass systems used.
Building a Biomass Facility
Keep in mind when selecting the location of the facility that you do not want a place with prevailing winds because smell and related complaints are often connected with waste processing facilities. Availability of electrical components is also an important factor that should be considered when setting up the facility they are needed for varied purposes:
Input—To power electrical motors, appliances, lights, etc.
Output—Where the Waste-to-Energy Plant produces electrical energy, an outlet system to feed the electrical grid is required.
About 120 tons of Fuel Stock is needed per day to make efficient use of the biomass facility and its system. For example, in Harvey County, KS, 35,000 people created 300 tons of garbage per day (about 150 tons after sorting). The County currently collects its waste stream sorting and recycling the components that are marketable. The types of fuel available are:
Trees, branches, yard clippings
Municipal waste and sewer sludge
High sulfur (junk) coal and more
Waste from industrial facilities
Steps Using rotary cascading bed combustion (RCBC) as an example, five modules will be needed: waste collection, material recovery and waste processing, RCBC fuel storage, RCBC combustion/boiler system and an electrical generation system.
Waste Collection—First, determine types and amounts of waste to be collected, then calculate heat values of various types of waste to be collected. Using these calculations, design a waste collection system to allow efficient use of entire biomass system.
Material Recovery Facility—Determine what types and amounts of wastes will be recycled. Based on this calculation, input tonnage per day and system time of operation, will waste storage be needed.
Combustible Fuel Storage—Based on previous calculations, will additional combustible fuels and necessary storage facility be needed? Additional combustible fuel may be needed for gaps in waste, non-cycled run time, long weekends, holidays, etc.
RCBC Combustion/Boiler System—Using fuel heat values and amounts, calculations can be made to gain maximum burn efficiency of single waste fuels, waste fuel combinations and/or waste fuel/auxiliary fuel combinations. Low, Average and High BTU values are calculated for various burn ratios to achieve maximum energy output from waste fuel input based on system capacities.
Electrical Generation System—Using previous calculations of operating efficiency and the output capacities of a condensing turbine generator, electricity output levels can be determined. Working with the local utility provider, ability to sell excess electricity to the local power grid is calculated.
Cost Benefit Analysis, ROI and Financing
Using all the calculations of operating expense and income calculations including waste fees, recycling fees and electricity generation fees, the overall profitability of the biomass facility can be determined. This, combined with the non-dollar value profits (land reclamation, CO2 decrease, increased recyclable content, etc.), will quickly prove the worth of the system.
Using the RCBC as an example, initial investment in a small system can range from $12,000,000 to $15,000,000 for a 150/ton/day system producing 6 megawatts that could power 1,500 average sized homes or 60.000 lbs of steam per hour for an industrial facility.
For a large biomass system, the initial Investment can range from $35,000,000 to $45,000,000 for a 300-600/ton/day system that produces 20 megawatts powering 5000 average sized homes.
Financing for biomass projects can be obtained through public and private sources or a combination of both. Types of financing options include:
Repayment terms range between 10 to 15 years based upon project structure
Finance payments can be made on either quarterly or semi-annual basis
Fixed and floating rate loans are available
As we learn more and more about the long-term requirements for conventional fuels throughout the world, and their finite supplies, it becomes of greater and greater importance to look for and find other practical sources of power. Certainly a great deal of development has been devoted to wind and solar power with great expectations for future success. Nuclear power is again at the forefront of discussion.
However, a significant, and substantial, source of power is readily available in every city and hamlet of the world: conversion of Waste-to-Energy—taking burdensome people, animal and production waste and cleanly converting it to electrical power through small unit power generation stations. Two key world problems, waste disposal and economical electrical generation, can be solved simultaneously through a clean and economical Waste-to-Energy facility.
Doug King is President of RCBC Global Inc. (Hendersonville, NC). For more than 25 years, the firm has been involved in waste management and use. They both have been at the forefront in the development and use of evolving technology for waste management, recycling and waste-to-energy conversion. Doug is a recognized expert in the design, installation and operation of Materials Recovery Facilities and is often called upon to consult, lecture and teach the most contemporary concepts on waste management systems and equipment use. He is a regular lecturer in Clemson University's continuing education program on solid waste management and recycling systems. For more information about an analysis of constructing and financing a biomass facility, contact Doug at (828) 696-2111 or e-mail email@example.com