Designing and building a large biomass bulk storage facility can be fraught with issues. Toro Shelters take a systems approach to delivering all of our bulk stores, from conception through to delivery and ongoing support. By examining all the process interfaces, both physical and with the wider stakeholder community. Over the whole life of the project we aim to get it right first time. The aim of this article is to take you through a logical journey to arrive at the right solution for your bulk storage needs.
Understanding the User’s Biomass Bulk Storage Needs
As with any engineering project, the most important phase is the requirements capture, get this wrong and the knock on effects will be disastrous!
The first stage of requirements capture is to develop a ‘User Requirement Document’. This is essentially a structured, high level document that captures what the user needs to achieve. Toro will ask some simple probing questions that may bring to light potential issues or alternative solutions. Some of the fundamental questions we would ask might include: “what material do you need to store?”. A fairly obvious question perhaps, but when followed with “and could your stored material change in the future?” can bring to light crucial information. Different materials will have different energy densities and energetic properties but importantly to us, physical properties.
Taking wood as a worked example:
- Wood chips have an angle of repose of 500 where for wood pellets it is closer to 400 – this will drive the design height of our structure.
- Therefore, a 20x20m store with 3m retaining walls will theoretically hold 2,080m3 of pellets or 2,440m3 of chips – This will drive the size of your structure.
- However, the density of the pellets is much than other material. The same sized storage facility might hold 1,144 tonnes of pellets but only 574 tonnes of wood chips. This will determine the retaining wall type for our structure.
The two images below show pre-cast, cast in ‘L’ shaped walls and precast panels supported by universal columns, two options available to our customers depending on their requirements.
The type of material stored will also dictate which regulations shall apply to the store; the Environment Agency’s ‘Fire Prevention Plan V.2’, released in March 2015. This document holds a wealth of information about pile sizes, separation, suppression systems and pollution control and is one of the first documents we will turn to.
As you can see from this example, thinking ahead, looking at the ‘whole life cycle’ of a storage facility can help to mitigate scope creep and additional cost in the future. The flow diagram below takes you through some of the typical questions we would seek to answer:
Defining the Bulk Store Solution
With the User Requirements defined, Toro will then develop a System Requirement Document. By knowing what constraints Toro and our clients are working with we can define how the structure needs to perform. Invariably, we will need to go through a process of ‘trading’ requirements to a reach a practicable solution taking into account functional requirements, safety factors, environmental concerns and, of course, price!
This is where we capture the User Requirements and ask the ‘so what?’ questions. Examining a recent example of one of Toro’s clients demonstrates the process best:
Case study: Biomass Bulk Store for Wood Pellets.
- The bulk store needs to store 2000m3 of wood pellets – so what?
- The structure must be at least 20x20m.
- The internal height must be at least 12m.
- Design will need to follow the EA’s Fire Prevention Plan guidelines – so what?
- We must accommodate a fire suppression system that can deliver sufficient water.
- The sprinklers must be 3m below the stored material.
- The design will need to facilitate secondary and tertiary firewater run-off containment
- Internal walls must offer a thermal barrier.
- The facility will be loaded by tipper lorries and unloaded by auger – So what?
- The doorway will need a minimum height of 10.5m to clear the extended tipper lorry.
- The structure must not only accommodate but facilitate the operation of the specified auger system.
The points above raise only a few of the vital questions posed, but they demonstrate the need to understand these issues at an early stage.
Designing the Bulk Store Solution
With the requirement defined and agreed with the customer and any wider stakeholders, Toro will build up an initial proposal. It is likely that we will have some user and system requirements concerning the aesthetic design of the structure, both for planning and simple preference. We will take these, along with the functional and structural requirements, to design a solution that will start as a ‘Sketchup’ image, albeit backed with engineering calculations.