CHALLENGE

Designing a thermal oxidizer with an attached steam generator recuperator requires careful balancing of combustion, air supply, and heat recovery. The key problem was ensuring complete waste destruction at the required 800°C while minimizing fuel consumption and optimizing steam generation.

BENEFITS

By integrating combustion, fluid flow, and heat recovery in a single model, Flownex enabled:

1. Rapid design iterations — engineers could test multiple air/fuel and heat recovery configurations in hours instead of weeks.

2. Quantified fuel savings — the optimal balance of fuel and secondary air was identified, reducing operating cost while still guaranteeing 800 °C for complete waste destruction.

3. Accurate steam generator recuperator sizing — ensuring required steam output without overdesign, saving both capital and operating costs.

4. Reduced risk in design decisions — the model gave confidence that waste would be destroyed while maximizing heat recovery, avoiding expensive oversizing or performance shortfalls.

SOLUTION

Flownex was used to build a single model capturing combustion, fluid flow, and heat transfer. Iterative scripts determined the correct fuel and air flows to achieve the destruction temperature and oxygen targets, while the recuperator section was sized to ensure efficient steam generation.

INTRODUCTION

Thermal oxidizers are widely used in the oil and gas industry to safely destroy hazardous waste streams at high temperatures. To improve efficiency, waste heat from the flue gas is often recovered in a steam generator recuperator. Accurately predicting combustion behavior, heat transfer, and fluid flow interactions in such systems is critical to ensure complete waste destruction, stable operation, and maximum energy recovery.

SYSTEM DESCRIPTION

The system consists of three main sections:

1. Natural gas burner – provides sufficient energy to create an 800°C environment for waste destruction.

2. Thermal oxidizer chamber – where the hazardous waste stream, containing its own oxygen supply, is injected and oxidized.

3. Steam generator recuperator – recovers heat from the flue gas to produce dry saturated steam at 1,750 kPag outlet pressure.

The waste gas typically requires 3–5% O₂ in the flue gas to ensure complete oxidation. A schematic of the system is shown in Figure 1.

OBJECTIVE OF SIMULATION

The objective was to use Flownex to:

1. Perform a complete heat and mass balance for the thermal oxidizer and attached steam generator recuperator.

2. Determine fuel and air requirements to maintain stable combustion and achieve target O₂ levels.

3. Size the steam generator recuperator to achieve the required steam quality and flue gas outlet conditions.

FLOWNEX MODEL

A Flownex model was developed that included:

1. Standard pipe elements for chambers and flow passages.

2. Compound components for natural gas combustion, air psychrometry, and gas property specification.

3. Utility components for fuel composition conversion, flue gas analysis, and excess air control.

The network was divided into three sections: burner, oxidizer, and steam generator recuperator as seen in Figure 2 below.

Data transfer links and Designer scripts were used to vary fuel, air, and flow rates until all performance targets were achieved.

DESCRIPTION OF SIMULATION

The simulation used an iterative three-step Designer procedure:

1. Burner fuel optimization – adjusting burner air and fuel to achieve ~1% O₂ concentration in the burner flue gas, ensuring stable combustion and efficient fuel use.

2. Oxidizer secondary air control – adding secondary air in the oxidizer chamber to reach the final 3–5% O₂ in the flue gas, guaranteeing complete oxidation of the waste stream.

3. Temperature control – varying fuel flow in the oxidizer to maintain the target chamber temperature of 800°C.

For the steam generator recuperator, the flue gas side was modelled for a desired outlet temperature of 255°C. Heat transfer was linked to the water side, and a script adjusted water flow until saturated steam was achieved at the outlet.

RESULTS

1. Fuel and air requirements were determined for stable combustion and complete waste destruction.

2. Chamber residence time was verified to be sufficient (>1 s) for the waste gas stream.

3. Steam generator recuperator sizing ensured dry saturated steam supply at 1,750 kPag, with flue gas cooled from 800°C to 255°C.

4. The model confirmed that heat recovery targets were achievable without compromising waste destruction efficiency.

CONCLUSION

This case study shows how Flownex can integrate combustion, fluid flow, thermodynamics, and heat transfer in a single model to solve complex process problems. The simulation provided a complete heat and mass balance for the thermal oxidizer and steam generator recuperator, enabling optimization of fuel usage, assurance of waste destruction, and efficient steam generation. The approach reduced design risk and demonstrated Flownex’s value as a reliable engineering tool in the oil and gas industry.