Automated Biochar Injection System

The goal of the project is to design a mobile BioChar (BC) injection system that will accept and inject BC into pressurized water lines in an accurate, controlled, and recorded manner in tandem with existing systems on the UIdaho Clean Water Machine with minimal adaptation of current systems.

=Problem Definition=

Background


Extensive algal blooms and phosphorous resource limitations are current problems faced by communities globally, primarily regarding agricultural fertilization and waste products. The University of Idaho Capstone teams in the past have partnered with Nexom and other entities to create the Clean Water Machine, an upward-circulating sand filtration system, to address nutrient pollution and purify the agricultural wastewater. Current research is being conducted by pumping biochar (biomass charcoal created by burning wood products and other organic materials) into the system to absorb more pollutants, especially phosphorous, from the wastewater. The BioChar can then be recovered and recycled as a fertilizer for soil. Our goal as a team is to create a system that integrates cohesively with the current Clean Water Machine and automates the biochar dosing process into the wastewater flow, so that more experiments and research may be conducted efficiently and effectively in the future. The completed project will be a mobile unit that accepts and injects BioChar into the pressurized water lines in an accurate, controlled, and recorded manner in tandem with the existing Clean Water Machine system with minimal adaptations. Our system will be completed by May 2019 as a fully functional product ready to be integrated into the Clean Water Machine's operations.

Deliverables
A system that will store the BC and maintain storage at consistent conditions

A system that will modify any purchased BC to specific parameters for the injection system

A method of transporting the BC to the influent water pipes

Automated and manual controls of the injection system 

Graphical I/O touch screen display 

A system for wetting and mixing the BC so the BC stays suspended for the specified contact time

A frame that will integrate and interface seamlessly with the existing frame on the Clean Water Machine

Functional Requirements
Deliver wet or dry BC with 15% accuracy, within 1.5 mg, and no under-dosing Operate quieter than 60 dB when at maximum capacity</li> Detect and account for variability in moisture content, consistency, and temperature</li> Must keep BC at constant conditions (temperature, moisture content, texture) </li>

Mechanical Requirements
 Space/Weight: 

Must fit on 40ft trailer with Clean Water Machine for transport</li> Machine footprint must not exceed 10 ft x 10 ft</li> Must have openings in frame for maintenance and access</li> The total BC injection system shall weigh no more than 300 lbs </li> Clean Water Machine, trailer set-up, and BC mechanism will not weigh more than 26000 lbs</li>

 Mounting: 

System shall be modular to allow for disassembly for travel</li> System shall mount to the current Clean Water Machine frame</li>

 Appearance: 

Labeled and laser-etched controls and hardware </li> LED’s included as indicators and decoration</li> Clear material is preferred especially in areas of change and flow</li> Neutral single colors (greens, blues, black, metal finish etc.; match logo of Clean Water Machine) </li>

 Durability: 

Hopper must handle load of at least 208 kg/m^3 of BC for three days with no refill </li> Pipe will withstand flow rate and pressure of 15 gal/min and 25 psi respectively</li> <li>System shall be designed to operate for 1 year without any scheduled maintenance </li> <li>No more than one 5-minute operation/maintenance check per day</li> <li>Tear down and rebuild in half a day to completely disassemble and reassemble</li> <li>Full operational capabilities in environments with ambient temperatures of 32°F to 110°F and humidity from 20-90%</li> <li>All electrical components shall be IP67 </li> <li>All material shall withstand corrosion and contact with water </li> <li>All components (including bearings) shall have 90% reliability</li>

Electrical Requirements
<li>Input will be 120V or 240V and controls shall operate at 24V and 4-20mA </li> <li>Touch-screen controls must last 12 hours of constant use while disconnected from main voltage source </li> <li>Touch-screen controls must last 24 hours without recharging </li>

Software Requirements
 Functionality: 

<li>Standard WIFI 802.11 and at least two USB 3.0 busses</li> <li>Must integrate with existing system</li> <li>Display must have 10-finger touch capacity capability</li> <li>Setting to switch between Automatic and Manual controls</li>

 User Interface: 

<li>Display flow-rate at inlet and outlet (gal/min) </li> <li>Display hopper capacity (grams), temperature (ºF), moisture content (%), and BC dose rate (g/mL) </li> <li>Performance indicators for malfunction and normal operation</li>

=Design Considerations=

Conditioning
As a solution for the BC inconsistencies in texture and particle size, a grinding system was added to the design below the hopper. Two stainless steel rollers with an adjustable distance between them are attached to a motor at a variable RPM. However during testing, as depicted in the following image, larger pieces of BC were not pulled through the grinders. This began clogging the hopper and preventing flow. To solve this problem, a dual milling process will be implemented. A similar two-roller system will be positioned above the original rollers; larger teeth will pull the BC through and break it into smaller pieces, which can subsequently be ground to powder in the second step.

Metering

 * Volumetric metering: rotating drum
 * Gravimetric verification: load cell

Injection
The influent water line is pressurized up to 18 psi. A venturi nozzle operates based on a change in liquid pressure when it flows through a constricted space. This provides continuous flow and can be easily adjusted to vary the output. It will be installed at the injection location in the system to overcome the back pressure from the transport between atmospheric pressure and pressurized pipes after the BC has been metered.

=Project Learning=

Clean Water Machine System


Currently, the BC is dosed into the Clean Water Machine in batches in the ratio of 6 kg per 50 gallons of influent water. This requires an operator to manually pour and stir the BC. This is inefficient and does not produce consistent dosing. The flow diagram to the right was provided by our client to describe how the BC can be monitored, dosed systematically, and integrated into the current Clean Water Machine design.

Fluidized Bed
One option explored for maintaining BC consistency was a fluidized bed for drying and mixing. A fluidized bed can produce a liquid effect in granular materials such as sand by distributing air flow from the base of its container. The team constructed a drying mechanism similar to a fluidized bed to test with sand and BC as a proof of concept for this method. PVC piping with 2 mm holes drilled at 45 degree angles 1 inch apart were sealed and connected to an air compressor. Ideally, the air would be heated, and therefore heat the BC while also keeping the powder in motion. However, during the tests with sand, the air flow was not enough to produce the floating effect. The test with BC was even less successful. The design only produced preferential flow in the powder, meaning the air was not distributed throughout the bulk. This was concluded to not be an effective design to reliably treat the BC evenly.

Moisture Content Experiments
Experimental plans have been written to test the BC density as a function of moisture content. Moisture content is calculated as the percent difference in mass from completely dried BC and the sample at different dry times. Metering can then be corrected for changes in BC density depending on moisture content. Additionally, lab measured moisture content will be compared to the samples' detected moisture content indicated by the moisture sensors to confirm their accuracy within 2%.

=Final Design=

Prototype
The prototype is currently being assembled.

=Validation=

=Team Members=

=Additional Documentation=

Client Interview Project Introduction

Concept Design Review

Engineering Release Review

Project Schedule

Meeting Agendas and Minutes

Team Contract

References