Mechanical Components

Mechanical plant components for material handling and process control.

Pump

Pumps for substrate transport, recirculation, and digestate processing in biogas plants.

Parameters

from pyadm1.components.mechanical import Pump

pump = Pump(
    component_id="pump1",
    pump_type="progressive_cavity",  # or "centrifugal", "piston"
    Q_nom=15.0,                      # Nominal flow rate [m³/h]
    pressure_head=50.0,              # Design pressure head [m]
    efficiency=None,                 # Auto-computed if None
    motor_efficiency=0.90,           # Motor efficiency (0–1)
    fluid_density=1020.0,            # Fluid density [kg/m³]
    speed_control=True,              # Variable-frequency drive
    name="Feed pump"
)

Pump Type Comparison

Type	Best for	Efficiency	Advantages	Disadvantages
Centrifugal	Low-viscosity liquids	65–75%	• High flow rates • Robust • Low maintenance	• Not self-priming • Poor with high viscosity • Efficiency drops with solids
Progressive Cavity	Viscous slurries	50–70%	• Handles high solids • Self-priming • Gentle transport	• Lower efficiency • Higher maintenance • Speed-dependent pressure
Piston	High-pressure applications	70–85%	• High-pressure capability • Precise flow control • Good efficiency	• Higher cost • More complex • Sensitive to solids

Sizing Guidelines

Flow-rate selection:

Plant size	Substrate feed [m³/d]	Pump Q_nom [m³/h]	Typical pressure [m]
Small	10–25	5–15	30–50
Medium	25–75	15–40	40–60
Large	75–200	40–100	50–80

Pressure-head considerations:

# Compute required pressure head
H_static = 5.0      # Vertical lift [m]
H_friction = 8.0    # Pipe friction losses [m]
H_process = 2.0     # Process pressure [m]
H_safety = 1.2      # Safety factor

H_required = (H_static + H_friction + H_process) * H_safety
# = 18.0 m

pump = Pump("pump1", Q_nom=15, pressure_head=H_required)

Outputs

{
    'P_consumed': 8.5,           # Power consumption [kW]
    'Q_actual': 10.0,            # Actual flow rate [m³/h]
    'is_running': True,          # Operating state
    'efficiency': 0.68,          # Current efficiency
    'pressure_actual': 48.5,     # Actual pressure [m]
    'speed_fraction': 1.0,       # Speed (0–1)
    'specific_energy': 0.85      # Energy per volume [kWh/m³]
}

Usage Example

# Progressive-cavity pump for substrate transport
pump = Pump(
    component_id="feed_pump",
    pump_type="progressive_cavity",
    Q_nom=15.0,
    pressure_head=50.0,
    speed_control=True
)

pump.initialize()

# Operate at 80% capacity
result = pump.step(
    t=0,
    dt=1/24,
    inputs={
        'Q_setpoint': 12.0,
        'enable_pump': True,
        'fluid_density': 1020,
        'pressure_head': 50
    }
)

print(f"Power: {result['P_consumed']:.1f} kW")
print(f"Flow: {result['Q_actual']:.1f} m³/h")
print(f"Efficiency: {result['efficiency']:.1%}")

Power Consumption

Pumps compute power based on the hydraulic formula:

P_hydraulic = ρ × g × Q × H / 1000  [kW]
P_shaft = P_hydraulic / η_pump
P_electrical = P_shaft / η_motor

Where:
- ρ = fluid density [kg/m³]
- g = 9.81 m/s²
- Q = flow rate [m³/s]
- H = pressure head [m]
- η = efficiency

Typical power consumption:

Flow [m³/h]	Head [m]	Pump type	Power [kW]
10	30	Centrifugal	2.5
10	50	Progressive cavity	4.5
15	50	Progressive cavity	6.8
20	60	Piston	10.5

Mixer

Mixers and agitators that maintain homogeneity in anaerobic digesters.

Parameters

from pyadm1.components.mechanical import Mixer

mixer = Mixer(
    component_id="mix1",
    mixer_type="propeller",          # or "paddle", "jet"
    tank_volume=2000.0,              # Tank volume [m³]
    tank_diameter=None,              # Auto-computed if None
    mixing_intensity="medium",       # "low", "medium", "high"
    power_installed=None,            # Auto-computed if None
    intermittent=True,               # Intermittent operation
    on_time_fraction=0.25,           # 25% on-time
    name="Main mixer"
)

Mixer Types

Type	Flow pattern	Best for	Power factor	Typical speed [rpm]
Propeller	Axial	Large tanks, liquid substrates	1.0×	40–100
Paddle	Radial	High solids, fibrous material	1.2×	20–60
Jet	Hydraulic	Recirculation mixing	1.5×	N/A (pump)

Mixing Intensity

Intensity	Specific power [W/m³]	Mixing time [min]	Application
Low	3	15–30	Liquid manure, low solids
Medium	5	8–15	Standard operation, energy crops
High	8	3–8	High solids, fibrous substrates

Sizing Example

# For a 2000 m³ digester with medium intensity
tank_volume = 2000  # m³
specific_power = 5  # W/m³ for medium intensity

P_required = (tank_volume * specific_power) / 1000  # kW
P_required *= 1.2  # safety factor for fibrous material
# = 12 kW

mixer = Mixer(
    "mix1",
    tank_volume=2000,
    mixing_intensity="medium",
    power_installed=15  # round up to standard size
)

Outputs

{
    'P_consumed': 12.5,          # Current power [kW]
    'P_average': 3.1,            # Time-averaged [kW]
    'is_running': True,          # Operating state
    'mixing_quality': 0.85,      # Quality index (0–1)
    'reynolds_number': 15000,    # Flow regime indicator
    'power_number': 0.32,        # Dimensionless power number
    'mixing_time': 8.5,          # Time to homogeneity [min]
    'shear_rate': 45.2,          # Average shear rate [1/s]
    'specific_power': 6.25,      # Power density [kW/m³]
    'tip_speed': 2.8             # Impeller tip speed [m/s]
}

Usage Example

# Medium-intensity propeller mixer
mixer = Mixer(
    component_id="mix1",
    mixer_type="propeller",
    tank_volume=2000,
    mixing_intensity="medium",
    intermittent=True,
    on_time_fraction=0.25  # 6 hours per day
)

mixer.initialize()

result = mixer.step(
    t=0,
    dt=1/24,
    inputs={
        'enable_mixing': True,
        'speed_setpoint': 1.0,
        'fluid_viscosity': 0.05  # Pa·s
    }
)

print(f"Power: {result['P_consumed']:.1f} kW")
print(f"Average power: {result['P_average']:.1f} kW")
print(f"Mixing quality: {result['mixing_quality']:.2f}")
print(f"Mixing time: {result['mixing_time']:.1f} min")

Intermittent Operation

Intermittent mixing reduces energy use:

# Comparison continuous vs. intermittent
# Continuous: 15 kW × 24 h = 360 kWh/day
# Intermittent (25%): 15 kW × 6 h = 90 kWh/day
# Savings: 270 kWh/day (75%)

mixer_continuous = Mixer(
    "mix_cont",
    tank_volume=2000,
    intermittent=False
)

mixer_intermittent = Mixer(
    "mix_int",
    tank_volume=2000,
    intermittent=True,
    on_time_fraction=0.25
)

# Both reach similar mixing quality

Recommended on-time fractions:

Substrate type	On-time	Total hours/day	Energy savings
Liquid manure	15–20%	3.6–4.8 h	80–85%
Energy crops	20–30%	4.8–7.2 h	70–80%
High solids	25–35%	6.0–8.4 h	65–75%
Fibrous material	30–40%	7.2–9.6 h	60–70%

Mixing-Power Calculation

Mixers compute power based on the power-number correlation:

# Mechanical power from power-number correlation
# P = Np * ρ * N³ * D⁵

N = operating_speed / 60.0  # Hz (revolutions/s)
D = impeller_diameter       # m

P_mech = power_number * fluid_density * N**3 * D**5 / 1000.0  # kW

# Account for motor efficiency (typically 85–95%)
motor_efficiency = 0.90
P_electrical = P_mech / motor_efficiency

# Limit to installed power
P_actual = min(P_electrical, power_installed)

Reynolds number for mixing:

Re = ρ * N * D² / μ

where:
- ρ = fluid density [kg/m³]  
- N = rotational speed [Hz]  
- D = impeller diameter [m]  
- μ = viscosity [Pa·s]  

Power number (depends on mixer type and Reynolds number):

• Propeller:
• Laminar (Re < 100): Np = 14.0 * Re^(-0.67)
• Transition (100 < Re < 10000): Np = 1.2 * Re^(-0.15)

• Turbulent (Re > 10000): Np = 0.32

• Paddle:

• Laminar (Re < 10): Np = 300.0 / Re
• Transition (10 < Re < 10000): Np = 8.0 * Re^(-0.25)
• Turbulent (Re > 10000): Np = 5.0

Mixing-Time Estimation

Based on the Nienow correlation:

θ_mix = C * (D_T/D)^α * (H/D_T)^β / N

where:
- C, α, β = constants depending on mixer type  
- D_T = tank diameter [m]  
- D = impeller diameter [m]  
- H = tank height [m]  
- N = rotational speed [Hz]  

Typical constants:

Mixer type	C	α	β
Propeller	5.3	2.0	0.5
Paddle	6.5	2.5	0.7
Jet	4.0	1.5	0.3

Integration Example

Complete Pump and Mixing Chain

from pyadm1.configurator import BiogasPlant, PlantConfigurator
from pyadm1.components.mechanical import Pump, Mixer
from pyadm1.substrates import Feedstock

# Setup
feedstock = Feedstock(feeding_freq=48)
plant = BiogasPlant("Mechanical System Plant")
config = PlantConfigurator(plant, feedstock)

# 1. Substrate feed pump
feed_pump = Pump(
    "feed_pump",
    pump_type="progressive_cavity",
    Q_nom=15.0,
    pressure_head=50.0,
    speed_control=True
)
plant.add_component(feed_pump)

# 2. Digester
digester, storage = config.add_digester(
    "main_digester",
    V_liq=2000,
    Q_substrates=[15, 10, 0, 0, 0, 0, 0, 0, 0, 0]
)

# 3. Main mixer
main_mixer = Mixer(
    "main_mixer",
    mixer_type="propeller",
    tank_volume=2000,
    mixing_intensity="medium",
    intermittent=True,
    on_time_fraction=0.25
)
plant.add_component(main_mixer)

# 4. Recirculation pump
recirc_pump = Pump(
    "recirc_pump",
    pump_type="centrifugal",
    Q_nom=50.0,  # Higher flow for recirculation
    pressure_head=10.0,  # Lower pressure
    speed_control=True
)
plant.add_component(recirc_pump)

# 5. Digestate pump
digestate_pump = Pump(
    "digestate_pump",
    pump_type="progressive_cavity",
    Q_nom=20.0,
    pressure_head=30.0
)
plant.add_component(digestate_pump)

# Energy system
config.add_chp("chp1", P_el_nom=500)
config.add_heating("heat1", target_temperature=308.15)

# Connections
config.connect("feed_pump", "main_digester", "liquid")
config.auto_connect_digester_to_chp("main_digester", "chp1")
config.auto_connect_chp_to_heating("chp1", "heat1")

# Simulate
plant.initialize()
results = plant.simulate(duration=30, dt=1/24, save_interval=1.0)

# Mechanical energy analysis
def mechanical_energy_analysis(results):
    """Analyze mechanical energy consumption."""
    final = results[-1]
    comp = final['components']

    # Pump energy
    feed_pump_energy = comp['feed_pump']['energy_consumed']
    recirc_pump_energy = comp['recirc_pump']['energy_consumed']
    digestate_pump_energy = comp['digestate_pump']['energy_consumed']
    total_pump_energy = feed_pump_energy + recirc_pump_energy + digestate_pump_energy

    # Mixer energy
    mixer_energy = comp['main_mixer']['energy_consumed']

    # Total mechanical energy
    total_mech_energy = total_pump_energy + mixer_energy

    # CHP production
    chp_energy = comp['chp1']['P_el'] * 30 * 24  # kWh

    # Parasitic load
    parasitic_fraction = total_mech_energy / chp_energy if chp_energy > 0 else 0

    return {
        'feed_pump': feed_pump_energy,
        'recirc_pump': recirc_pump_energy,
        'digestate_pump': digestate_pump_energy,
        'total_pump': total_pump_energy,
        'mixer': mixer_energy,
        'total_mechanical': total_mech_energy,
        'chp_production': chp_energy,
        'parasitic_fraction': parasitic_fraction,
        'net_energy': chp_energy - total_mech_energy
    }

analysis = mechanical_energy_analysis(results)
print("\nMechanical energy analysis:")
print(f"Feed pump: {analysis['feed_pump']:.0f} kWh")
print(f"Recirculation pump: {analysis['recirc_pump']:.0f} kWh")
print(f"Digestate pump: {analysis['digestate_pump']:.0f} kWh")
print(f"Total pumps: {analysis['total_pump']:.0f} kWh")
print(f"Mixer: {analysis['mixer']:.0f} kWh")
print(f"Total mechanical: {analysis['total_mechanical']:.0f} kWh")
print(f"Parasitic load: {analysis['parasitic_fraction']:.1%}")
print(f"Net energy production: {analysis['net_energy']:.0f} kWh")

Optimization Strategies

1. Pump Optimization

def optimize_pump_sizing(Q_required, H_required, pump_type="progressive_cavity"):
    """Optimize pump sizing for efficiency."""

    # Size for 80–90% of nominal load (highest efficiency)
    Q_nom = Q_required / 0.85

    # Add safety margin for pressure head
    H_nom = H_required * 1.2

    pump = Pump(
        "optimized_pump",
        pump_type=pump_type,
        Q_nom=Q_nom,
        pressure_head=H_nom,
        speed_control=True  # VFD for part-load optimization
    )

    return pump

# Example: 12 m³/h required at 40 m head
optimized = optimize_pump_sizing(12.0, 40.0)
print(f"Optimized pump size: {optimized.Q_nom:.1f} m³/h")

2. Mixing Optimization

def optimize_mixing_strategy(substrate_type, tank_volume):
    """Pick the optimal mixing strategy based on substrate."""

    strategies = {
        'liquid_manure': {
            'intensity': 'low',
            'on_time_fraction': 0.20,
            'mixer_type': 'propeller'
        },
        'energy_crops': {
            'intensity': 'medium',
            'on_time_fraction': 0.25,
            'mixer_type': 'propeller'
        },
        'high_solids': {
            'intensity': 'medium',
            'on_time_fraction': 0.30,
            'mixer_type': 'paddle'
        },
        'fibrous': {
            'intensity': 'high',
            'on_time_fraction': 0.35,
            'mixer_type': 'paddle'
        }
    }

    strategy = strategies.get(substrate_type, strategies['energy_crops'])

    mixer = Mixer(
        "optimized_mixer",
        mixer_type=strategy['mixer_type'],
        tank_volume=tank_volume,
        mixing_intensity=strategy['intensity'],
        intermittent=True,
        on_time_fraction=strategy['on_time_fraction']
    )

    return mixer, strategy

# Example: fibrous substrates
mixer, strategy = optimize_mixing_strategy('fibrous', 2000)
print(f"Optimized mixing strategy:")
print(f"- Type: {strategy['mixer_type']}")
print(f"- Intensity: {strategy['intensity']}")
print(f"- On-time: {strategy['on_time_fraction']:.0%}")

3. Energy Minimization

def minimize_mechanical_energy(plant_config):
    """Strategies to minimize mechanical energy use."""

    strategies = []

    # 1. Use intermittent mixing
    strategies.append({
        'name': 'Intermittent mixing',
        'saving': 0.70,  # 70% savings
        'implementation': 'on_time_fraction=0.25'
    })

    # 2. VFDs for pumps
    strategies.append({
        'name': 'VFD for part-load operation',
        'saving': 0.30,  # 30% savings at part load
        'implementation': 'speed_control=True'
    })

    # 3. Proper sizing
    strategies.append({
        'name': 'Optimal sizing',
        'saving': 0.15,  # 15% via efficiency optimization
        'implementation': 'Q_nom = Q_required / 0.85'
    })

    # 4. Lower mixing intensity where possible
    strategies.append({
        'name': 'Adjusted mixing intensity',
        'saving': 0.40,  # 40% via lower intensity
        'implementation': 'mixing_intensity="low" for liquid substrates'
    })

    total_potential = sum(s['saving'] for s in strategies)

    print("Energy-minimization strategies:")
    for s in strategies:
        print(f"- {s['name']}: {s['saving']:.0%} savings")
        print(f"  Implementation: {s['implementation']}")

    return strategies

strategies = minimize_mechanical_energy({})

Troubleshooting

Problem: Pump Delivers Insufficient Flow

Diagnosis:

pump_result = pump.step(0, 1/24, {'Q_setpoint': 15, 'enable_pump': True})

if pump_result['Q_actual'] < 0.8 * pump_result.get('Q_setpoint', 15):
    print("Low pump flow - check:")
    print(f"- Current efficiency: {pump_result['efficiency']:.1%}")
    print(f"- Pressure head: {pump_result['pressure_actual']:.1f} m")
    print(f"- Is the pump correctly sized for the application?")

    # Check for overload
    if pump.speed_fraction > 1.0:
        print("- WARNING: pump overloaded!")

Solutions:
- Increase pump size if consistently overloaded
- Reduce friction losses in piping
- Check for blockages or wear

Problem: Mixer Consumes Too Much Energy

Diagnosis:

mixer_result = mixer.step(0, 1/24, {})

specific_power = mixer_result['P_consumed'] / mixer.tank_volume  # kW/m³

if specific_power > 6.0:  # upper bound for medium intensity
    print(f"High specific power: {specific_power:.1f} W/m³")
    print("Optimization options:")

    if not mixer.intermittent:
        print("- Enable intermittent operation (70% savings)")

    if mixer.mixing_intensity == "high":
        print("- Reduce to medium intensity if possible")

Solutions:

# Implement intermittent operation
mixer_optimized = Mixer(
    "mix1",
    tank_volume=mixer.tank_volume,
    mixing_intensity="medium",
    intermittent=True,
    on_time_fraction=0.25  # 75% energy savings
)

Problem: Poor Mixing Quality

Diagnosis:

if mixer_result['mixing_quality'] < 0.7:
    print(f"Low mixing quality: {mixer_result['mixing_quality']:.2f}")
    print(f"Mixing time: {mixer_result['mixing_time']:.1f} min")
    print(f"Reynolds number: {mixer_result['reynolds_number']:.0f}")

    if mixer_result['reynolds_number'] < 1000:
        print("- Laminar flow - increase speed or impeller size")

    if mixer_result['mixing_time'] > 30:
        print("- Long mixing time - increase intensity or on-time")

Solutions:
- Increase mixing intensity for difficult substrates
- Extend on-time for intermittent operation
- Consider larger impeller or higher speed

Best Practices

1. Size pumps for optimal efficiency
2. Operate at 80–90% of nominal load

3. Use VFDs for variable load demands

4. Implement intermittent mixing

5. 25% on-time for most applications

6. Adjust to substrate type

7. Regular maintenance

8. Monitor pump efficiency over time

9. Check mixer wear

10. Optimize system design

11. Minimize piping losses

12. Correct pump placement

13. Monitor energy consumption

14. Track parasitic load
15. Target: <10% of CHP production

Next Steps

• Biological Components: Digester and process control
• Energy Components: CHP and heating systems
• Feeding Components: Storage and dosing
• API Reference: Detailed class documentation