A major hazard in chemical production and storage of chemicals is loss of thermal control, which can lead to destruction and release of toxic substances. A systematic risk analysis is essential in order to define the critical limits of temperature, dosing, storage temperature etc. A systematic risk assessment must include the following stages.
- Compilation of basic data (physical and chemical properties, reactivity data, interactions between chemicals, equipment data etc.)
- Define system (boundaries of safe process conditions)
- Identify hazards ( e.g. Check lists, Hazard and operability studies(HAZOP))
- Assess Risks (estimate severity and likelihood)
- Select risk reduction measures( e.g. technical, organizational, personnel)
- Remaining risks
Thermal process safety data of chemical reactions requires knowledge of the thermodynamics and kinetic properties of both wanted and unwanted reactions. Thermal process safety for physical operations (e.g. discharge, distillation) normally requires the thermodynamics and kinetic properties of unwanted reactions.
The basic questions to be asked in understanding of thermal data can be summarized as follows. e.g.
- What quantity of energy release is considered to be in itself dangerous?
- How can the DTad, potential adiabatic temperature increase, be used to determine a worst case scenario and its consequences?
- How can the TMRad, time to maximum rate adiabatic, can be used to determine the probability?
- How can the thermal data of the wanted and unwanted reactions be combined to develop cooling failure scenario and its criticality?
- How can decomposition reactions be characterized?
- How does one determine if a decomposition reaction is autocatalytic?
Chilworth has a fully equipped laboratory to determine the thermal data necessary for thermal process safety and storage of chemicals, evolved gas collection and analysis, physical properties testing and transportation requirements testing under the United Nations guidelines. The professionals at Chilworth have many years of industrial experience and expertise in thermal process safety and can provide total solutions to process and operational hazard analysis from compilation of basic data to solving thermal process safety requirements.
Powder Layer Screening Test
The powder layer test is used to evaluate the thermal stability of powders and dusts in dryers where heated air is circulated over a powder layer. Consequently, this test is also known as the air-over-layer test. It is intended to simulate the conditions to which materials are exposed in various types of dryers, including tray, band, and cross-flow. This test also simulates the conditions to which residual powder deposits in all types of dryers may be exposed.
Bulk Solid Screening Test
The Bulk Solid Test is used to evaluate the thermal stability of bulk solids, powders, and dusts during drying and related operations. It is intended to simulate the conditions to which materials are exposed when they collect in certain types of dryers or downstream in hoppers, silos, drums, or bags.
Aerated Solid Screening Test
The Aerated Powder Test is used to evaluate the thermal stability of powders and dusts during drying operations in which a heated air stream passes through the material, such as in circulating band and fluidized bed dryers.
Isothermal Test – Basket Test
While screening tests are useful for identifying a potential thermal stability hazard, more exacting isothermal tests are necessary to establish safe operating temperatures. Isothermal Basket Tests can be used to identify the minimum onset temperature of exothermic activity for a powder or dust sample. Further, since tests are conducted using at least three (3) sizes of basket, extrapolation techniques can be used to determine the maximum safe operating or storage temperature for virtually any vessel size or geometry.