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 the algae growth and purify the agricultural wastewater. Current research is being conducted by pumping BioChar (Bio-mass charcoal, created by burning wood products and other organic materials) into the system in an effort to absorb more chemicals (namely phosphorous) from the wastewater. The BioChar is ideally then filtered out, collected, and mixed into the soil in an attempt to recycle some of the lost phosphorous and create a way to fertilize crops without needing to mine a limited resource. Our goal as a team is to create a system that integrates cohesively with the current Clean Water Machine and automates the process of dosing the BioChar 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
 Strength: 

Load sensor shall withstand a range of 0.5 mg - 5 g </li> Hopper must handle load of at least 208 kg/m^3 of BC </li> Pipe will withstand flow rate and pressure of 15 gal/min and 25 psi respectively</li>

 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> <li>Neutral single colors (greens, blues, black, metal finish etc.; match logo of Clean Water Machine) </li>

 Durability: 

<li>System shall be designed to operate for 1 year without any scheduled maintenance </li> <li>Refill hopper no more than once every three days <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> <li>Components will withstand at least 5 years of constant use</li>

Electrical Requirements
<li>Input will be 120V or 240V</li> <li>Controls shall operate at 24V and 4-20mA</li> <li>Pi will be powered by 5V 2.1A USB</li> <li>Touch-screen controls must last 12 hours of constant use while disconnected from main voltage source </li> <li>Pi back-up battery must last 12000 mAh</li> <li>Touch-screen controls must last 24 hours without recharging </li>

Software Requirements
 Functionality: 

<li>Standard WIFI 802.11 </li> <li>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>In-field programmability (empty buttons created for programming dosage of additional chemicals) </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>Hopper capacity error/warning message and indicator at 15% capacity </li> <li>Performance indicators for malfunction and normal operation</li>

Production
<li>Prototype must be built for testing by February 1, 2019 </li> <li>Two physical devices created by May 10, 2019</li> <li>Cost to build a POC prototype shall not exceed $2500</li>

=Design Considerations= All three of the following design include three common areas: BC storage, conditioning, and metering. The hopper for storing the BC must hold enough BC to operate for three days without refilling. It must also not be bulky and must be weatherproof. It will include an auger to transport the BC into the conditioning system.

The BC must have consistent texture and moisture content when it reaches the metering system. Our design will therefore include a dryer, dehumidifier, and mixer. It must produce the same conditions regardless of external environment. It also include an auger to transport the BC into the metering system.

The options for metering systems can be found under the Project Learning section of this site.

Design 1
Our first design is consistent with typical powder dosing system at a wastewater facility. The hopper, dryer, and metering line dose into a conical container, whose shape creates mixing of the BC with water. Spray nozzles above the funnel provide access points if the operator needed to dose other types of chemicals simultaneously. The progressive cavity displacement pump also assists with mixing the BC.

However, these type of pumps are generally very expensive and difficult to find one appropriate for this scale of treatment. The numerous components in this design reduce settling of the BC, but also introduce many moving parts that could malfunction or wear out quickly from abrasion. The size and space requirements of this design are also unlikely to fit within the given constraints while remaining accessible for repair.

Design 2
In our second design, the BC is metered into a sloped container and washed out using water from the influent piping. A ball valve opens, allowing the water from the influent to flow through after the BC has been metered. This valve then closes and a check valve opens simultaneously with an air compressor pushing the water-BC slurry back into the influent pipe.

This is more simple and condense, has fewer moving parts, and is lower cost than the initial design. However, timing between the two valves is critical, and malfunction or clogging would completely disrupt the flow. It is also a design without much mixing of the BC into the water, which may cause the BC to clump or be left behind on the container. Another significant issue is the introduction of compressed air into the system. The purpose of the air is to match the pressure of the influent water pipe to push the BC out of the container. However, any air that continues into the piping much be removed or it would interfere with the rest of the treatment process.

Design 3
The final version of the third design was the team's suggested prototype. Two parallel sloped floor containers receive BC from the metering system and intermittently dose into the influent pipes to creates a more continuous dosing. This system is also directly in line with the influent water, although could be bypassed if necessary. The metering system is timed so that the BC is dropped into the chamber when both three-way valves are closed. One three-way valve switches the incoming water between the two chambers, and the other three-way valve alternates which chamber is emptied back in line with the pipes. A constant pressure tank and pressure regulator is supplied so that the removal of water from the influent pipe does not drastically lower the pressure further down the pipe. And air release valve is included for when the machine is first started, since the pipes will not have any water in them when not in use.

Considerations when moving forward with this design include eliminating areas that the BC may settle, timing the dosing and valves exactly and for startup operation, and calculating the flow requirements so as not to disrupt the pressure in the influent pipes.

=Project Learning=

Clean Water Machine System


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

Our role is to create an entire system including the interface with the current set up, the biochar storage, biochar condition control, dose metering, flow into the Clean Water Machine water lines, and the signals and controls required to do so.

Pumps
Our clients identified the pumping mechanism as a significant challenge in moving biochar. Because it is a granular material which does not dissolve in water, it often clogged pumps and the small particles cause pump parts to wear quickly or malfunction. Our initial assumption for this dosing system was that we would need to find the optimal pump type to avoid disruptions in flow. Peristaltic pumps are easily controlled and flow varied, but often have too narrow of tubing which results in significant clogging. Reciprocating and diaphragm pumps also clump and clog solids very easily, resulting in the pump not operating correctly. The current Clean Water Machine team also attempted to use a centrifugal pump. Although this has benefits such as the mixing motion, there are many parts involved, and the team had prior difficulty with this type.

The team also toured the |Moscow Water Reclamation and Reuse Facility in Moscow, ID, to see how this treatment process dosed powder polymer. This facility used large positive displacement pumps, which was recommended to us to scale down for our project. Both lobe rotary and progressive cavity positive displacement pumps are effective with viscous fluids and can produce a constant flow. Although usually more expensive than other pump types, the team determined that the progressive cavity pump fit our requirements best because it had fewer parts that may wear down, included rotary mixing motion, and was commonly implemented in similar industrial applications.

Metering
Venturi Nozzle:

A venturi nozzle operates based on a change in liquid pressure when it flows through a constricted space. This type of metering provides continuous flow and can be easily adjusted to vary the output. However, slurry tends to clog and volumetric metering is difficult. This is still our primary design suggestion, as it is the most practical for moving the BC. Another consideration when using the venturi nozzle is that it will need to start and stop as it moves between the two different BC containers.

Syringe Pump: A syringe pump would be the most accurate way to dose BC. However, BC properties may cause it to clog and become less accurate as it is continuously dosed. Another significant consideration is the dosing rate possible with this type of metering. Syringe pumps are typically used for small scale applications, and the syringes themselves have small capacities.

Small auger:

An auger is a simple, inexpensive form of dosing BC. Although there are few parts involved, the motion against the dry BC could quickly damage the surface of the equipment. Most significantly, although an auger is continuous, it is not an accurate dosage, and any differences in BC properties could impact the dose rate.

Scale/Cup:

A simple method of dosing is a scale and cup set up. BC would be dosed gravimetrically into the cup, which would be very accurate and eliminate areas for BC clogging. However, this would be challenging in our application since it would be noncontinuous and must be completely separated from the external environment.

Compressed tablets: A different approach to dosing would be to compress the BC into very accurate tablets and insert these into the influent water. The issues with this method is that the chunks must be entirely dispersed evenly into the water, and cannot clump or clog other areas. Although consistent and simple, this will most likely not be an option for the Clean Water Machine.

Electronics
The following electrical components were researched for the project related to sensors and controls:

<li>Ultrasonic transmitters and ultrasonic horns were researched as a way to keep BC particles suspended</li> <li>Automation Direct will be implemented for the controls, as it is already used on the CWM for other operations</li> <li>Arduino Uno will be the microcontroller used for both testing and the final prototype</li> <li>A Raspberry Pi will be programmed for the touch screen display for the operator </li> <li>We designed a circuit to test BC static charge properties</li> <li>USB, ethernet, and Wi-Fi will integrate the injection system to the CWM </li>

=Final Design=

=Validation=

=Team Members=

=Additional Documentation=

Project Schedule

Client Interview Project Introduction

Meeting Agendas and Minutes

Team Contract

References