Project 747: TinyML Blast Furnace Hot Metal Desulfurization Exhaust Gas Baghouse Rotary Feeder Thermal Expansion Radial Clearance Guard

Project 747: TinyML Blast Furnace Hot Metal Desulfurization Exhaust Gas Baghouse Rotary Feeder Thermal Expansion Radial Clearance Guard

1. 1.
   Executive Summary & Architectural Overview

During primary hot metal desulfurization in integrated steelmaking, powdered calcium carbide (CaC_2), lime (CaO), and magnesium (Mg) reagents are injected into molten iron ladles (1,350^\circ\text{C}\text{--}1,450^\circ\text{C}). The process generates massive volumes of pyrophoric, abrasive exhaust gas loaded with ultra-fine reagent dust. The particulate capture baghouse operates at elevated temperatures (180^\circ\text{C}\text{--}280^\circ\text{C}) under pulsed reverse-air cleaning.

Rotary airlock feeders installed beneath the baghouse discharge hoppers must seal positive/negative system pressures while metering abrasive reagent dust into pneumatic transfer lines:

Severe Differential Thermal Expansion: The cast steel housing cools rapidly via convective ambient losses, while the heavy internal multi-vane rotor absorbs intense sensible heat from the hot gas stream. The resulting differential thermal expansion causes the tight nominal radial clearance (0.15\ \text{mm} to 0.25\ \text{mm}) to shrink to zero, triggering catastrophic rotor seizure and motor drive trips.

Abrasive Galling & Rotor Blade Gouging: As clearance decreases below critical particle size (d_{50} ≈ 45\ \mu\text{m}), hard carbide particles become wedged between the rotor tips and the housing bore, causing severe abrasive gouging (>85,000$ replacement cost).

Dust Blowout & Explosion Hazard: Loss of seal integrity causes hot combustible gas leakage, presenting severe secondary dust explosion hazards in the baghouse sub-structure.

The TinyML Rotary Feeder Thermal Expansion Radial Clearance Guard is an edge-AI electro-mechanical protection controller powered by a Teensy 4.1 (600 MHz ARM Cortex-M7). It interfaces with non-contact high-temperature eddy current displacement sensors (Micro-Epsilon) rated to 300^\circ\text{C}, dual multi-point K-type thermocouples via MAX31856 cold-junction compensators, an AD7606 16-bit ADC, and a VFD drive speed trimmer. Running real-time differential thermal expansion finite-difference models, predictive clearance estimators, and a TinyML neural seizure classifier, the guard dynamically commands emergency casing cooling air and trims rotor speed to avoid catastrophic mechanical seizure.

+---------------------------------------------------------------------------------------------------+

| PROJECT 747: ROTARY FEEDER CLEARANCE GUARD BLOCK DIAGRAM |

+---------------------------------------------------------------------------------------------------+

| |

| [BLAST FURNACE DESULFURIZATION BAGHOUSE HOPPER DISCHARGE: 250 deg C, CaC2 DUST, ABRASIVE] |

| +-----------------------------------------------------------------------------------------+ |

| | Rotary Airlock Feeder (10-Vane Hardox Rotor, Cast Carbon Steel Casing) | |

| | [High-Temp Eddy Current Probes (Gap Top & Bottom)] [Dual K-Type Thermocouple Array] | |

| +-----------------------------------------------------------------------------------------+ |

| | (0-10V Analog Gap Signal, 0-1.0 mm) | (Microvolt K-Type Leads) |

| v v |

| +---------------------------------------+ +---------------------------------------+ |

| | Industrial Analog Front-End Buffer | | MAX31856 Precision Thermocouple AFEs | |

| | (AD8606 Rail-to-Rail Low Noise Op-Amp)| | (Cold-Junction Compensated, SPI Bus) | |

| +---------------------------------------+ +---------------------------------------+ |

| | | |

| +-----------------------+ +---------------------+ |

| v v |

| +-----------------------------------------------------------------------------------------+ |

| | TEENSY 4.1 EMBEDDED CONTROLLER (600 MHz ARM Cortex-M7, 1MB RAM, 8MB Flash) | |

| | - Core 1: Non-Blocking 1 kHz Gap Dynamics & Thermal Model: delta_r = r0 alpha dT | |

| | - TinyML Classifier: 8-input -> 12-hidden -> 3-class Seizure Risk Predictor | |

| | - Hardware Watchdog Timer: Watchdog_t4 (500 ms Timeout Window) | |

| | - Deterministic FSM: NORMAL -> CLEARANCEWARN -> SPEEDTRIM -> EMERGENCYCOOLINGTRIP | |

| +-----------------------------------------------------------------------------------------+ |

| | | |

| v (4-20 mA Analog Output) v (Optocoupled Relay Outputs) |

| +---------------------------------------+ +---------------------------------------+ |

| | VFD Speed Trim Controller | | Pneumatic Emergency Cooling Actuators | |

| | (AD5421 Industrial 4-20 mA Loop DAC) | | (High-Flow Compressed Air Injection) | |

| +---------------------------------------+ +---------------------------------------+ |

| | | |

| v v |

| [Rotary Feeder VFD Drive] [Baghouse Plant DCS / SCADA] |

+---------------------------------------------------------------------------------------------------+

1. 1.
   Mathematical Models & Governing Equations

Equation 1: Differential Thermal Expansion of Rotor vs Housing

The radial expansion \Delta r_{rotor} of the rotor cylinder (radius R_0 = 250\ \text{mm}) subjected to gas temperature T_{rotor} is: $\Delta r_{rotor} = R_0 · α_{rotor} · (T_{rotor} - T_0) The expansion \Delta r{housing}$ of the outer housing bore subjected to skin temperature $T{housing} is: \Delta r_{housing} = R_0 · α_{housing} · (T_{housing} - T_0)$ Where:

α_{rotor} ≈ 12.0 × 10^{-6}\ \text{K}^{-1} (Hardox / high-chromium steel).

α_{housing} ≈ 11.5 × 10^{-6}\ \text{K}^{-1} (Cast steel).

T_0 = 20^\circ\text{C} (Assembly reference temperature).

The instantaneous operating radial clearance C(t) is: $C(t) = C_0 + \Delta r_{housing}(t) - \Delta r_{rotor}(t) - δ_{eccentricity}(t) Where C0 = 0.22\ \text{mm}$ is nominal cold clearance, and $\delta{eccentricity}$ accounts for shaft deflection and bearing runout.

Equation 2: Critical Particle Pinch Shear Stress

When clearance C(t) drops below maximum abrasive particle diameter d_{max} ≈ 85\ \mu\text{m}, particle wedging induces mechanical shear stress \tau_{pinch}: $\tau_{pinch} = (E_{eff})/(1 - \nu^2) · ≤ft((d_{max} - C(t))/(d_{max})\right)^{3/2} If \tau_{pinch} > 450\ \text{MPa}$, rotor surface yielding and abrasive scoring begin instantaneously.

Equation 3: TinyML Seizure Hazard Probability

The onboard feedforward classifier processes an 8-dimensional feature vector: $\mathbf{x} = [C_{top}, C_{bot}, T_{rotor}, T_{housing}, (dC)/(dt), (dT)/(dt), I_{motor}, \omega_{rpm}] The neural network computes softmax probability P_{seizure} \in [0.0, 1.0]$:

P_{seizure} < 0.20: Safe operating condition.

0.20 ≤ P_{seizure} ≤ 0.65: Clearance warning; command VFD speed reduction by 25%.

P_{seizure} > 0.65: Imminent seizure lock; fire pneumatic emergency cooling jacket, trip motor drive.

1. 1.
   Bill of Materials (Dual Currency: INR ₹ & USD $)

Item

Component Description

Qty

Unit Cost (INR ₹)

Total Cost (INR ₹)

Unit Cost (USD $)

Total Cost (USD $)

1

Teensy 4.1 Development Board (600MHz ARM Cortex-M7)

1

₹3,450

₹3,450

$41.50

$41.50

2

Micro-Epsilon High-Temp Eddy Current Sensor (0-1.0mm)

2

₹24,000

₹48,000

$289.00

$578.00

3

MAX31856 Precision Thermocouple Converter Breakout

2

₹1,100

₹2,200

$13.20

$26.40

4

K-Type Inconel-Sheathed Mineral Insulated Thermocouples

2

₹850

₹1,700

$10.20

$20.40

5

AD5421 Industrial 4-20mA Loop-Powered DAC Module

1

₹1,850

₹1,850

$22.20

$22.20

6

AD8606 Precision Low-Noise Dual Operational Amplifier

1

₹380

₹380

$4.60

$4.60

7

Phoenix Contact 24VDC Industrial Solid-State Relay

2

₹950

₹1,900

$11.40

$22.80

8

High-Pressure Solenoid Air Valve (Asco 1-inch, 24VDC)

1

₹6,800

₹6,800

$82.00

$82.00

9

Mean Well HDR-60-24 Industrial DIN-Rail Power Supply

1

₹1,650

₹1,650

$19.80

$19.80

10

IP66 Heavy Cast Aluminum Enclosure with Vibration Dampers

1

₹4,200

₹4,200

$50.50

$50.50

Total

Complete Hardware Subassembly

₹72,130

$868.20

1. 1.
   Mechanical & Electrical Assembly

Eddy Current Sensor Tap Installation: Drill and tap two M12x1 probe ports into the rotary feeder casing at top dead center (12\ \text{o'clock}) and bottom dead center (6\ \text{o'clock}). Use ceramic insulating sleeves to isolate sensors thermally.

Thermocouple Well Placement: Embed one thermocouple tip into the casing wall (2\ \text{mm} from inner bore) and point an infrared pyrometer or trailing-wire RTD at the rotor hub.

Pneumatic Jacket Plumbing: Mount four vortex air cooling nozzles symmetrically around the casing outer periphery, connected to an industrial 7 bar compressed air line through the Asco solenoid valve.

Vibration Isolation: Mount the Teensy 4.1 instrumentation panel on silicone anti-vibration dampers on the structural steel column > 2\ \text{meters} away from the shaker frame.

1. 1.
   Deterministic Finite State Machine (FSM)

STATEBOOT (0): Arm Watchdogt4 (500 ms), initialize SPI peripherals, read calibration offsets.

STATENORMALRUN (1): Feeder operating smoothly. C_{min} ≥ 0.12\ \text{mm}, P_{seizure} < 0.20. VFD commanded at nominal 100% speed (20 mA).

STATECLEARANCEWARN (2): 0.08\ \text{mm} ≤ C_{min} < 0.12\ \text{mm} or 0.20 ≤ P_{seizure} ≤ 0.65. Output 4-20 mA speed trim (reducing VFD speed to 60%), assert warning beacon.

STATEEMERGENCYCOOLING (3): C_{min} < 0.08\ \text{mm} or P_{seizure} > 0.65. Actuate high-flow compressed air cooling solenoids, trim speed to 20%.

STATESEIZURETRIP (4): C_{min} ≤ 0.04\ \text{mm} for > 50\ \text{ms}. Deassert motor drive interlock in < 10\ \text{ms}, halting feeder to prevent rotor gouging.

STATELOCKEDOUT (5): Requires manual clearance verification after cool-down.

1. 1.
   Calibration & Verification Checklist

Feeler Gauge Shimming Calibration: With rotor cold, insert precision 0.10\ \text{mm}, 0.15\ \text{mm}, 0.20\ \text{mm} feeler shims; adjust eddy current scaling factors until error is < 0.005\ \text{mm}.

Thermocouple Reference Test: Verify MAX31856 temperature readings match a calibrated dry-well calibrator within ± 0.5^\circ\text{C} up to 300^\circ\text{C}.

TinyML Response Time Test: Feed synthetic multi-variable vectors; verify neural classifier completes execution in < 80\ \mu\text{s}.

Emergency Stop Latency: Simulate a sudden clearance collapse (< 0.04\ \text{mm}); verify motor interlock relay opens in < 8.5\ \text{ms}.

Pinout & Wiring Specifications

Project 747: Pinout and Wiring Guide

1. 1.
   Master Interconnect Schedule

Subsystem

Signal Name

Teensy 4.1 Pin

Sensor / Actuator Pin

Electrical Spec

Cable & Shielding Specifications

Eddy Current Top

GAP_TOP

Pin A0 (14)

Sensor Output (+)

0-3.3V Scaled Analog

High-temp Teflon shielded twisted pair

Eddy Current Bot

GAP_BOT

Pin A1 (15)

Sensor Output (+)

0-3.3V Scaled Analog

High-temp Teflon shielded twisted pair

Thermocouple 1

CS1

Pin 10

MAX31856 CS

3.3V SPI Chip Select

Point-to-point trace

Thermocouple 2

CS2

Pin 9

MAX31856 CS

3.3V SPI Chip Select

Point-to-point trace

SPI Interface

SCK

Pin 13

MAX31856 SCK

5 MHz SPI Clock

Guarded trace

SPI Interface

MISO

Pin 12

MAX31856 SDO

3.3V SPI Data In

Guarded trace

Cooling Actuator

COOL_SOL

Pin 6

Solid-State Relay (+)

3.3V Optoisolated Drive

Industrial 24V wiring

Motor Interlock

MOTOR_TRIP

Pin 5

VFD Safe Torque Off

3.3V Fail-Safe Active-HIGH

Twisted pair to VFD STO terminal

Diagnostics

LED

Pin 13

Onboard LED

3.3V Logic Drive

Direct trace

1. 1.
   ASCII Electrical Schematic

+3.3V VCC

|

+--------------+------------------+

| |

+---------------+ +---------------+

| Teensy 4.1 | | Dual Eddy |

| Controller | | Current Probes|

| | +---------------+

| Pin A0 <----+---| Top Probe (0-3.3V)

| Pin A1 <----+---| Bot Probe (0-3.3V)

| |

| Pin 10 -----+--> [MAX31856 #1 CS] ---> Casing Thermocouple

| Pin 9 ------+--> [MAX31856 #2 CS] ---> Gas Stream Thermocouple

| Pin 13/12 --+--> SPI Bus

| |

| Pin 6 ------+-->+---------------+

| Pin 5 ------+-->+---------------+

| | | VFD STO Relay |---> To Feeder Motor VFD Safe Torque Off

+---------------+ +---------------+

|

GND

1. 1.
   Industrial Grounding & Shielding Protocol

Use separate conduit runs for the 480V VFD motor lines and the millivolt-level eddy current probe cables (> 300\ \text{mm} physical clearance).

Terminate all eddy current sensor cable shields at the instrument enclosure ground lug only to avoid ground loops.

Arduino C++ Firmware Source Code

/*
 * Project 747: TinyML Blast Furnace Hot Metal Desulfurization Exhaust Gas 
 *              Baghouse Rotary Feeder Thermal Expansion Radial Clearance Guard
 * Platform: Teensy 4.1 (600 MHz ARM Cortex-M7)
 * Firmware: Non-Blocking Real-Time Clearance Estimator with Watchdog_t4
 */

#include <Arduino.h>
#include <SPI.h>
#include <Watchdog_t4.h>

WDT_T4<WDT1> wdt;

// --- PIN DEFINITIONS (Teensy 4.1) ---
const uint8_t PIN_GAP_TOP_ADC    = A0;  // Eddy Current Probe Top (0-3.3V scaled)
const uint8_t PIN_GAP_BOT_ADC    = A1;  // Eddy Current Probe Bottom (0-3.3V scaled)

const uint8_t PIN_MAX31856_CS1   = 10;  // Thermocouple 1 (Casing)
const uint8_t PIN_MAX31856_CS2   = 9;   // Thermocouple 2 (Gas Stream)

const uint8_t PIN_COOLING_VALVE  = 6;   // High-Flow Compressed Air Solenoid
const uint8_t PIN_MOTOR_TRIP     = 5;   // Active-HIGH Fail-Safe Motor Interlock
const uint8_t PIN_STATUS_LED     = 13;  // Onboard Diagnostic LED

// --- THRESHOLDS & PHYSICAL CONSTANTS ---
const float GAP_WARN_MM         = 0.120f; // 120 microns warning
const float GAP_COOL_MM         = 0.080f; // 80 microns emergency air injection
const float GAP_TRIP_MM         = 0.040f; // 40 microns hard trip to prevent galling
const float VOLTS_PER_MM        = 3.3f / 1.0f; // 0-3.3V corresponds to 0-1.0mm

enum SystemState {
    STATE_BOOT = 0,
    STATE_NORMAL_RUN,
    STATE_CLEARANCE_WARN,
    STATE_EMERGENCY_COOLING,
    STATE_SEIZURE_TRIP,
    STATE_LOCKED_OUT
};

SystemState currentState = STATE_BOOT;

// --- TELEMETRY STRUCT ---
struct FeederTelemetry {
    float gapTop_mm;
    float gapBot_mm;
    float minGap_mm;
    float tempCasing_C;
    float tempGas_C;
    float seizureRiskProb;
    uint8_t vfdSpeedPercent;
};

FeederTelemetry telemetry;

// Timing variables
unsigned long lastSampleMicros   = 0;
unsigned long lastTelemetryMillis = 0;
const unsigned long SAMPLE_PERIOD_MICROS = 1000; // 1 kHz sampling
const unsigned long TELEMETRY_PERIOD_MS = 100;   // 10 Hz telemetry

void wdtCallback() {
    digitalWrite(PIN_MOTOR_TRIP, LOW); // De-energize motor drive on crash
}

float readEddyGap(uint8_t pin) {
    // 16-sample oversampled analog read
    uint32_t sum = 0;
    for (int i = 0; i < 16; i++) {
        sum += analogRead(pin);
    }
    float v = ((float)sum / 16.0f) * (3.3f / 1023.0f);
    return (v / VOLTS_PER_MM);
}

float evaluateTinyMLSeizureRisk(float gap, float tCasing, float tGas) {
    // Lightweight perceptron evaluating non-linear temperature & gap gradients
    float deltaT = tGas - tCasing;
    float normalizedGap = (gap - 0.040f) / 0.180f; // 0.0 to 1.0
    float logit = -3.5f * normalizedGap + 0.015f * deltaT - 0.5f;
    // Sigmoid activation
    float prob = 1.0f / (1.0f + expf(-logit));
    return prob;
}

void setup() {
    pinMode(PIN_COOLING_VALVE, OUTPUT);
    pinMode(PIN_MOTOR_TRIP, OUTPUT);
    pinMode(PIN_STATUS_LED, OUTPUT);
    pinMode(PIN_MAX31856_CS1, OUTPUT);
    pinMode(PIN_MAX31856_CS2, OUTPUT);

    digitalWrite(PIN_COOLING_VALVE, LOW); // Air valve closed
    digitalWrite(PIN_MOTOR_TRIP, HIGH);   // Motor enabled
    digitalWrite(PIN_STATUS_LED, LOW);
    digitalWrite(PIN_MAX31856_CS1, HIGH);
    digitalWrite(PIN_MAX31856_CS2, HIGH);

    Serial.begin(115200);
    SPI.begin();
    analogReadResolution(10);

    // Watchdog Setup
    WDT_timings_t config;
    config.trigger = 5.0;
    config.timeout = 0.5; // 500 ms hard watchdog
    config.callback = wdtCallback;
    wdt.init(config);

    currentState = STATE_NORMAL_RUN;
}

void loop() {
    wdt.feed();
    unsigned long currentMicros = micros();

    // 1 kHz Non-blocking Sampling
    if (currentMicros - lastSampleMicros >= SAMPLE_PERIOD_MICROS) {
        lastSampleMicros = currentMicros;

        telemetry.gapTop_mm = readEddyGap(PIN_GAP_TOP_ADC);
        telemetry.gapBot_mm = readEddyGap(PIN_GAP_BOT_ADC);
        telemetry.minGap_mm = (telemetry.gapTop_mm < telemetry.gapBot_mm) ? telemetry.gapTop_mm : telemetry.gapBot_mm;

        // Simulated temperatures (in real deployment, queried via MAX31856 SPI)
        telemetry.tempCasing_C = 185.0f;
        telemetry.tempGas_C    = 240.0f;

        telemetry.seizureRiskProb = evaluateTinyMLSeizureRisk(telemetry.minGap_mm, telemetry.tempCasing_C, telemetry.tempGas_C);

        // State Machine
        switch (currentState) {
            case STATE_NORMAL_RUN:
                digitalWrite(PIN_MOTOR_TRIP, HIGH);
                digitalWrite(PIN_COOLING_VALVE, LOW);
                digitalWrite(PIN_STATUS_LED, LOW);
                telemetry.vfdSpeedPercent = 100;

                if (telemetry.minGap_mm <= GAP_TRIP_MM || telemetry.seizureRiskProb > 0.85f) {
                    currentState = STATE_SEIZURE_TRIP;
                } else if (telemetry.minGap_mm <= GAP_COOL_MM || telemetry.seizureRiskProb > 0.65f) {
                    currentState = STATE_EMERGENCY_COOLING;
                } else if (telemetry.minGap_mm <= GAP_WARN_MM || telemetry.seizureRiskProb > 0.35f) {
                    currentState = STATE_CLEARANCE_WARN;
                }
                break;

            case STATE_CLEARANCE_WARN:
                digitalWrite(PIN_STATUS_LED, HIGH);
                digitalWrite(PIN_COOLING_VALVE, LOW);
                telemetry.vfdSpeedPercent = 60; // Trim speed to reduce frictional heat

                if (telemetry.minGap_mm <= GAP_TRIP_MM || telemetry.seizureRiskProb > 0.85f) {
                    currentState = STATE_SEIZURE_TRIP;
                } else if (telemetry.minGap_mm <= GAP_COOL_MM || telemetry.seizureRiskProb > 0.65f) {
                    currentState = STATE_EMERGENCY_COOLING;
                } else if (telemetry.minGap_mm > GAP_WARN_MM && telemetry.seizureRiskProb < 0.25f) {
                    currentState = STATE_NORMAL_RUN;
                }
                break;

            case STATE_EMERGENCY_COOLING:
                digitalWrite(PIN_STATUS_LED, HIGH);
                digitalWrite(PIN_COOLING_VALVE, HIGH); // Open vortex cooling air
                telemetry.vfdSpeedPercent = 30;

                if (telemetry.minGap_mm <= GAP_TRIP_MM || telemetry.seizureRiskProb > 0.85f) {
                    currentState = STATE_SEIZURE_TRIP;
                } else if (telemetry.minGap_mm > GAP_COOL_MM && telemetry.seizureRiskProb < 0.50f) {
                    currentState = STATE_CLEARANCE_WARN;
                }
                break;

            case STATE_SEIZURE_TRIP:
                digitalWrite(PIN_MOTOR_TRIP, LOW); // DE-ENERGIZE MOTOR DRIVE
                digitalWrite(PIN_COOLING_VALVE, HIGH); // Keep cooling
                digitalWrite(PIN_STATUS_LED, HIGH);
                telemetry.vfdSpeedPercent = 0;
                currentState = STATE_LOCKED_OUT;
                break;

            case STATE_LOCKED_OUT:
                digitalWrite(PIN_MOTOR_TRIP, LOW);
                break;

            default:
                currentState = STATE_NORMAL_RUN;
                break;
        }
    }

    // Telemetry Stream (10 Hz)
    unsigned long currentMillis = millis();
    if (currentMillis - lastTelemetryMillis >= TELEMETRY_PERIOD_MS) {
        lastTelemetryMillis = currentMillis;

        Serial.print("STATE:");
        Serial.print((int)currentState);
        Serial.print(",MIN_GAP_UM:");
        Serial.print(telemetry.minGap_mm * 1000.0f, 1);
        Serial.print(",RISK_PROB:");
        Serial.print(telemetry.seizureRiskProb, 3);
        Serial.print(",SPEED_%:");
        Serial.println(telemetry.vfdSpeedPercent);
    }
}