# Biogas and Landfill CHP Gensets: Fuel Gas Treatment, Methane Number and ISO 8528

> Engineering guide for biogas, landfill and sewage gas cogeneration gensets covering fuel gas conditioning, Methane Number (MN) knock limits, thermal recovery, and ISO 8528 COP continuous duty.

- **Category:** Generator Systems & Energy Production
- **Author:** Voltformer Power Generation & Cogeneration Engineering
- **Publication Date:** 2026-09-16
- **Reading Time:** 9 min read
- **Key Tags:** #Biogas Generator, #Landfill Gas, #CHP Cogeneration, #ISO 8528 COP, #Methane Number
- **Canonical URL:** https://voltformer.com/articles/biogas-and-landfill-chp-generator-sets-methane-number-fuel-treatment-iso-8528
- **Markdown Source:** https://voltformer.com/articles/biogas-and-landfill-chp-generator-sets-methane-number-fuel-treatment-iso-8528.md

### 1. Gas Quality Challenges in Biogenic Energy Conversion

Reciprocating gas engine generator sets operating on anaerobic digester biogas, sewage gas or landfill gas face severe fuel quality variations compared to pipeline natural gas. High moisture ($100\%$ relative humidity at digester outlet), hydrogen sulfide ($H_2S$ up to $5000\text{ ppm}$), and volatile organic silicon compounds (**siloxanes**) cause rapid lubricating oil degradation, abrasive silica ($SiO_2$) cylinder deposits, and turbocharger corrosion.

### 2. Methane Number, Heating Value & Engine Derating

| Gas Characteristic | Natural Gas (Pipeline) | Agricultural Biogas | Landfill / Sewage Gas |
|---|---|---|---|
| **Methane Content ($CH_4$)** | 90 - 98 vol% | 50 - 65 vol% | 38 - 52 vol% |
| **Lower Heating Value ($LHV$)** | $36 - 38\text{ MJ/Nm}^3$ | $18 - 23\text{ MJ/Nm}^3$ | $14 - 18\text{ MJ/Nm}^3$ |
| **Methane Number ($MN$)** | 70 - 85 | **$> 100$ (CO2 knock inhibitor)** | **$> 110$** |
| **Pre-Treatment Required** | Basic filtration | Dehumidification + Biological H2S | Deep chilling ($+4^\circ\text{C}$) + Carbon bed |
| **Duty Rating (ISO 8528-1)** | Baseload / Peaking | **Continuous Operating Power (COP)** | **Continuous Operating Power (COP)** |

The electrical power output from gas flow is calculated by:

$$ P_e = \eta_e \cdot \dot{V}_{gas} \cdot LHV_{gas} \quad [\text{kW}] $$

Where:
- $\eta_e$ is the electrical efficiency of the lean-burn gas engine ($40\% - 44\%$ for modern turbocharged units).
- $\dot{V}_{gas}$ is the normalized volumetric gas feed rate in $\text{Nm}^3/\text{h}$.
- $LHV_{gas} = \frac{\%CH_4}{100} \cdot 35.8\text{ MJ/Nm}^3$.

### 3. Combined Heat and Power (CHP) Thermal Integration

In biogas cogeneration installations, overall energy efficiency exceeds $88\%$ by recovering two primary heat streams:
1. **High-Temperature Circuit:** Exhaust gas heat exchanger produces hot water ($90/70^\circ\text{C}$) or low-pressure steam ($180^\circ\text{C}$) recovering $\approx 40\%$ of fuel thermal energy.
2. **Low-Temperature Circuit:** Engine jacket water, lubricating oil plate cooler and first-stage mixture intercooler deliver warm water ($60/45^\circ\text{C}$) for digester tank heating.

### 4. Specification Requirements for Gas Engine Procurement

- Mandate gas dehumidification chiller ($+4^\circ\text{C}$ dew point) and activated carbon filter upstream of engine throttle.
- Require automated air-fuel ratio ($A/F$) control with fast oxygen sensor ($\lambda = 1.6 - 1.8$ lean-burn combustion) to maintain $NO_x < 250\text{ mg/Nm}^3$ (TA-Luft 2021).
- Verify alternator insulation class H with Class F temperature rise ($105\text{ K}$) for $24/7$ continuous baseload operation.
- Specify anti-corrosive stainless-steel piping and nickel-plated gas mixer for corrosive landfill gas duty.

*Reference: ISO 8528-1:2018; ISO 3046-1; DVGW Code of Practice G 262; TA-Luft 2021.*

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