Introduction

In 2015, a cogeneration plant was commissioned in Monterrey, Mexico, to supply our client’s metallurgical and cardboard production facilities. With an installed capacity of 14.4 MW, this plant was consolidated as an essential energy pillar for the operation of the different industrial units of the complex.

The facility was designed under a combined cycle scheme, which allows it to efficiently generate both the steam required for the thermal processes and the electrical energy needed to operate the associated paper mill and metallurgical facility.

AITESA participated in the project as supplier and responsible for the assembly of the heat recovery boiler, a key equipment in the cogeneration system. This boiler takes advantage of the thermal energy contained in the exhaust gases of the gas turbine to produce process steam, thus maximizing the overall efficiency of the energy system.

The main challenge was to integrate a cogeneration system that maximizes energy efficiency by making the most of the waste heat generated in the paperboard production process. The goal was to direct this heat to a cogeneration plant capable of producing steam for both internal consumption and electricity generation, thus optimizing fuel use.

AITESA Solution

The solution provided by AITESA involves the installation of a natural circulation boiler designed to generate steam at two pressure levels: 40 bar and 6 bar. It is equipped with an afterburner system using 10 MW auxiliary burners, which allows reaching a maximum production of 32.6 t/h of superheated steam at 400 °C and 40 bar, together with 2 t/h of saturated steam at 6 bar for auxiliary services.

The boiler is structured in the following functional modules:

• High pressure superheater: in charge of raising the temperature of the saturated steam to the required superheating conditions.
• High pressure evaporator: module where water evaporation takes place by natural circulation, connected to its respective high pressure boiler.
• High pressure economizer: preheats the feed water before it enters the high pressure boiler, improving thermal efficiency.
• Low pressure evaporator: transforms water into saturated steam at low pressure, with its associated boiler.
• Common economizer for high and low pressure: preheats the feed water and distributes it to the low pressure boiler and to the high pressure economizer, optimizing the thermal distribution.

In addition to the afterburner system and the main modules, AITESA also supplied all the auxiliary equipment necessary for the correct operation of the system: feed pumps, continuous purge flash tank, purge cooling tank, steam silencers and the complete instrumentation for the control and supervision of the boiler.

This design allows not only to feed thermal processes, but also to drive a turbine for electricity production, significantly increasing the overall efficiency of the plant.

Results

• Energy savings: Reduction of fossil fuel consumption by integrating cogeneration.
• On-site power generation: Contribution to self-generation of electricity with the steam turbine.
• Optimization of thermal processes: Steam available at two pressure levels improves operational versatility.
• Reduced emissions: More efficient use of energy reduces environmental footprint.

In June 2013, a contract was awarded for the supply of the boiler and its auxiliary equipment, which was delivered during 2014. The plant started operating in 2015 and has been operating satisfactorily ever since.