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Specialized TRAX Studies -
Ethylene Cracking Furnace

Modifying unique site configurations can rapidly introduce a host of complications and uncertainty. TRAX Energy Solutions can provide a dynamic engineering study to optimize plant operation and control logic for a variety of clients and specialized process types.

Here's one example where TRAX helped a client determine the impacts of a process change and provided recommendations to improve plant behavior.

Example Study

TRAX was retained by a client to examine the impact of adding a gas turbine and associated ductwork and dampers to two existing ethylene cracking furnaces. To predict the behavior of the future configuration during a gas turbine trip, TRAX built high-fidelity process and controls models to examine both the steady-state and dynamic behaviors of the plant. The steady-state analysis highlighted issues such as incorrect fan sizing, control set points, and excess O2 control. The dynamic analysis provided insight into how the system responded to unexpected events, and showed that it was possible to smoothly transition to ambient air combustion without tripping the furnace on a gas turbine trip.

Furnace owners can have good motivation for adding a gas turbine to an ethylene cracking furnace. A gas turbine can improve plant efficiency, improve ethylene yield percentage, and provide power for plant operations.

In the client’s model, the future configuration was established with the gas turbine discharging into the ethylene cracking furnace. The hot exhaust gas was added to the ambient combustion air and the gas turbine was used to augment the electrical load of the plant. The model predicted temperatures at the furnace radiant coil outlet and the convection section outlet, as well as associated dynamic radiant and convective heat loads. The control system was tuned to run to steady-state as effectively as possible. Once tuned, the control system achieved steady-state within five minutes.

The control system response was analyzed, looking for issues with pressures, flows, and excess O2, during the dynamic event and in the resulting steady-state condition. Based on the results of these analyses, TRAX formulated and tested an alternate set of control logic that allowed for a smooth and efficient transition to ambient air combustion and demonstrated these TRAX-proposed controls to the client. Several key changes improved the plant response:

Fuel valve demand: TRAX suggested a cross-limiter and tuned the fuel gas setpoint after a turbine trip.
Air flow damper control: TRAX modified the airflow set point based on ethylene yield percentage and the status of the gas turbine. Another cross-limiter and a kicker circuit were proposed.
ID fan demand: TRAX tuned the furnace pressure set points in response to the trip data.

Areas of Concern

TRAX can help clients address a number of concerns for a variety of process types and unique or unusual configurations.

Thermal Stress

Heat generated by the gas turbine can add stress on the furnace. A study can include a focus on the thermal stress of the boiler and turbine. Reduced thermal stress leads to better availability.

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Damage Prevention

Good controls help avoid situations that include the possibility of equipment damage. This includes conditions like turbine differential expansion excursions and steam temperature excursions.

Environmental Compliance

TRAX can optimize controls to prevent or reduce the occurrence of certain conditions, such as venting through bypass stacks or bypassing environmental equipment in emergency scenarios.

Control/Process Test Bed

With a study, it is possible to test control systems before adding them to a live unit. They are a valuable tool for testing new controls.

Agility in Startup and Shutdown

A study can be used to reduce stress on equipment and increase ramp speed during startup.

Heat Rate Awareness

A study can be used to examine heat rate in different scenarios. Promoting savings in fuel helps the environment and economics of the unit, both crucial to long-term sustainability.

A TRAX study can help protect vulnerable equipment by predicting and mitigating severe pressure and temperatures during transient events. A study will also present recommendations for the best future configuration and suggestions for controls improvements of plant operation.

By addressing potential risks from a position of knowledge, plant owners can successfully leverage the benefits of making process changes while mitigating potential risks effectively. These studies can be especially useful for new technologies or complex process types, such as:

Carbon capture addition
Coal to natural gas conversion
Sulfur dioxide scrubber addition
NOx removal and SCR addition

Specialized TRAX Studies - Ethylene Cracking Furnace