Coffee Roaster Filtration System

The goal of the project is design, fabricate, and test a low-cost air filtration system for an industrial batch coffee roaster. The system will reduce visible smoke output by 95% and mitigate odor transmission. The system is adaptable to Diedrich Roaster's IR-5 and IR-12 models, and serves as a more affordable alternative to their catalytic oxidizer.

=Problem Definition=

Background


Roaster Emissions

The unique chemical compositions of coffee beans result in diverse emissions during the roasting process. These emissions can be generalized into two categories: Gaseous emissions and particulate matter (PM). In batch roasting, the primary gaseous release of concern is carbon dioxide, factoring for approximately 10% of gaseous emissions up to as high as 25% in roasters which utilize thermal oxidizers in post-treatment. A small amount of carbon monoxide is released as well, but at near-negligible rates. Both carbon monoxide and carbon dioxide are relatively color- and odorless. The main cause of smell and smoke in roasting comes from various classes of volatile organic compounds (VOC). VOCs are any number of organic (containing carbon) compounds that have a relatively low boiling point, near room temperature (volatile). Methane is a common VOC, but the are myriad compounds which fall within the category. Due to coffee's complex chemical nature, identifying the specific VOC's emitted is a challenge, as each bean will release a slightly different combination. Particulate matter (PM) refers to solid matter, typically waste carbon, ejected during oxidation. In coffee roasting, this primarily appears in the form of chaff.

EPA Regulations

In commercial applications, the EPA has a series of standards businesses which roast their own coffee must adhere to. However, smaller companies and private roasters are not bound by these emissions requirements. EPA standards, while very possible to achieve, are expensive and prohibitive towards smaller companies or individuals early in their roasting career, and few solutions exist on the market that are both EPA-compliant and affordable.

Thermal Oxidizer

Because roasting happens below the point of combustion, the exhaust from a roaster is largely unburned matter. This is evidenced in the amount of VOC's reached, as many of the compounds are flammable. Thermal oxidisers exploit this issue by providing an afterburn to the exhaust of a roaster. By raising the exhaust temperature significantly and exposing the outgoing material to open flame, a thermal oxidizer is able to convert many of the harmful VOCs into CO2 and H20, the products of complete combustion in hydrocarbons. Thermal oxidisers are one of the most common aftertreatment systems in the coffee roasting industry due to their effectiveness, and used in many other commercial settings, such as air control in factories. A common enhancement in these systems is the catalytic oxidizer, wherein the exhaust stream is forced through a catalytic converter.

Deliverables
The filter must be able to accept flow rates typical of the IR-5 and IR-12 and maintain acceptable filtration levels. The filter must be self-supported and capable of existing as a standalone system. The design must be low-cost, constructed primarily of sheet metal, and low-maintenance. Finally, the system should be innovative, setting itself apart from other filtration systems on the market.

Specifications
=Previous Design Considerations=

Electrostatic Precipitator (ESP)
An electrostatic precipitator uses electric charge to attract pollutants as flow passes through. (Pictures added soon)

Pros: The system is tried and true.

Cons: ESP efficiency is very temperature dependent.

Electrostatic Filter
An electrostatic filter operates on the same principles as ESPs, but instead of having an external power source, generates static charge from particulate as it passes through.

Pros: Low cost.

Cons: Low efficiency, low temperature range.

Wet Filter
Wet filters are essentially sponges.

Pros: Low cost, lowers temperatures.

Cons: Short lifetime.

Wet Scrubber
A wet scrubber uses Venturi principles and the power of condensation to remove particulate.

Pros:Lowers temperature.

Cons: Less efficient for its size.

=Project Learning=

The Coffee Community
Especially being located in the PNW, hobby roasters are very common. Many have created their own ingenious and inexpensive ways to address the problem of affordable filtration. Coffee roaster forums have played an invaluable role in the design process by suggesting possible solutions and testing methods, pointing towards helpful research, and answering any questions that the team could think of.

Roasting Process
=Current Design Process=

Main Filter - Cyclonic Wet Scrubber
The cyclonic wet scrubber operates on the same principles as a standard wet scrubber with some modifications. (More explanation will be added soon). The current development on the cyclonic wet scrubber is a proof-of-concept venture tube, water injector, and cyclone chamber system.

Secondary Filter - Electrostatic Precipitator
Determination of the post-scrubber filter has not been determined yet.

=Validation=

Opacity Meter
Opacity meters are used to determine the level to which content in air affects visibility, typically through use of a light transmitter that pulses a signal and compares either the reflected light or the transmission loss against a control level. Opacity meters are common in diesel fuel research and soot mitigation, and the UI used one for its Biodiesel program, but the meter has since been lost. A fabricated opacity meter design is in the works for use on the project.

The opacity meter is designed to be an inline meter. The transmitter is a simple white LED, and the receiver is a TSL2561 Lux sensor. The lux sensor was chosen due to its high range, relative sensitivity, and gain settings. The receiver and transmitter are placed opposite one another inside a matte black pipe, with prescribed diameter to fit the outlet piping. The matte black surface keeps light from bouncing within the sensor, allowing for higher accuracy.

The sensor outputs to an Arduino Uno, which also supplies power for the transmitter and receiver. When attached to a computer, the Arduino can either write data to a text file or pipe to the serial monitor. The lux sensor outputs a voltage response that can be mapped on a 0-100 scale; additionally, a lux library can be installed to convert the output to lumens using Bouguer's Law.

Smoke Generator
A challenge with testing any filtration system is being able to properly simulate the conditions the filtration system will encounter. Because the UI does not have the proper infrastructure for housing a temporary IR-12 roaster, a substitute system had to be improvised. The smoke generator is a simple combustion cave. A heating element is placed in the bottom of a heat-proof rigid container (in our case a 30 gallon oil drum) with a mesh bed slightly above it, where the combustion material rests. An inlet fan controls incoming air and outgoing flow rate. The team is currently debating what the heating element should be - coal/wood chips, an oven element, or a propane/CNG burner, but once determined, progress will be posted.

Testing Procedure
As the test equipment and instrumentation have not yet been finished, specifics of the test procedure can not yet be determined. however, the general procedure is as such:  Cover bed with combustion material   Secure smoke generator seal and engage fan on low power   Activate heating element and wait until outflow reaches operational temperatures   Vary fan power to operational flowrate   Measure intake and exhaust opacities at 3, 5, 8, and 11 minutes 

=Meet the Team=

=Documentation Archive= Project Schedule

Meeting Minutes

Presentations

=References=