The stack and emissions monitoring

How does The stack and emissions monitoring work, step by step?

1. 1

   Step 1: Take the height and location from the consent

   Stack height and position come from dispersion modelling carried out during consenting and agreed with the environmental regulator. They are fixed inputs to the project, not variables. Where aviation or navigation interests are affected, marking and lighting requirements are established at the same time. The team confirms the agreed height and position against the current layout at the start of detailed design, because layout changes made for other reasons can put the stack somewhere the modelling did not assume.

2. 2

   Step 2: Choose the stack form and design the foundation

   The designer selects the form - a self-supporting steel shell, a steel flue within a concrete windshield, or a flue carried by the plant structure - based on height, the number of flues, the site conditions, maintenance access and cost. The foundation is designed for a tall, slender structure where wind governs, so overturning and dynamic behaviour matter more than weight. Ground investigation under the stack is treated seriously, and the holding-down arrangement is designed as a fatigue sensitive detail rather than as ordinary anchorage.

3. 3

   Step 3: Build the foundation and set the holding-down arrangement

   The foundation is a substantial reinforced concrete element, commonly piled. Holding-down bolts or anchor assemblies are set on independent frames, surveyed before the pour and monitored during it, because the tolerance on them is tight and there is no adjustment available afterwards. Concrete is placed and cured under a thermal control plan where the pour is large. The completed foundation is surveyed and the as-built positions recorded and issued before erection begins.

4. 4

   Step 4: Erect the stack

   Erection is either by lifting complete sections into place with a large crane, or by building up from the base using jacking or climbing methods where crane capacity or access will not allow full height lifts. The method is chosen early because it affects the design of the sections, the joints and the temporary works. Verticality is checked continuously as the structure rises, and temporary stability and wind limits during erection are designed and stated rather than judged. Working at height dominates the whole activity.

5. 5

   Step 5: Complete the lining, coating and protection systems

   The internal surface is lined or coated to resist the flue gas condition it will see, and the external surface is protected against the weather. Lightning protection and earthing are installed and tested. Where aviation or navigation marking is required, painting and lighting are completed to the stated requirements, along with the power supply and the monitoring that keeps the lighting available. Drainage from the base of the flue is provided and routed to collection.

6. 6

   Step 6: Fit permanent access, platforms and lifting provision

   The stack needs safe permanent access for the whole life of the plant, for monitoring equipment maintenance, for calibration work, for lighting maintenance and for inspection. Ladders or a lift, intermediate landings, the monitoring platform and any provision for lifting equipment up the structure are all designed and installed as part of the works. Rescue arrangements are considered as part of that design. These are much cheaper to build in than to add.

7. 7

   Step 7: Install the monitoring equipment and its sampling arrangements

   Sampling points, the analysers and their housing, the heated lines, the power supplies, the cabling and the data links are installed to the design agreed for the permit. Sampling positions are located where the regulator requires them and the reference measurement points are provided alongside. The equipment is commonly supplier scope with the site providing the installation, the services and the environmental conditions the analysers need. Data routing to the plant systems and to reporting is set up and proved.

8. 8

   Step 8: Calibrate, prove and hand over to the operator

   The monitoring system is calibrated and proved by specialists, with the arrangements and records that the operator's permit requires, and the reporting path is demonstrated end to end. This is done before the plant runs commercially, because the operator cannot run without working monitoring. The stack and the monitoring system are turned over as systems in the normal way, and from turnover the monitoring installation belongs to the operator and is maintained under their regime rather than touched by construction.