Biodiesel production has no more or less fire hazard than an oil refinery. Plant personnel at all levels need to be vigilant and totally informed, realizing that what they do not know can lead to disaster.
In my background of 23 years of operations and 41 years of plant design and construction, I have witnessed seven serious fires and two explosions. One victim spent four hours in brain surgery but survived. Another missed death by minutes. Each accident involved ignorance. Biodiesel plants and oil refineries are not for the ignorant—or the inattentive.
Is there any operator who does not know that all materials in a biodiesel plant can burn and also explode? Still, fires occur too often and the results are often disastrous. Costs, legal issues and lost time after a fire are very difficult to overcome. As educator Derek Bok once said, “If you think education is expensive, try ignorance.” Are there ways to reduce the risk and severity of fires? For starters, a plant safety manual is critical.
We all know the fire triangle’s three sides: oxygen, fuel and ignition.
Oxygen is as important for us as carbon dioxide is for plant life; it cannot be removed or reduced except inside tanks using inert gas.
The fuel leg of the triangle is a fertile field for wise decisions. The most hazardous material is obviously alcohol. A good source of information on safety in handling this volatile chemical is the Methanol Institute and its manual (www.methanol.org). A listing of methanol incidents, pages 133-147, deserves study; note the number of fires and causes—often maintenance and hot work—and spills, which could have led to disastrous fires. The number of fatalities is shocking.
Extinguishing methanol fires requires understanding methanol-water solubility. Methanol mixtures of 25 percent or higher will burn. Dikes around methanol tanks need to be higher to contain diluted methanol. Plant and animal oils have high flash points, but once burning they provide great energy, leading to total disaster.
Ignition sources deserve our total attention during design and construction—and daily thereafter. Building, electrical and fire codes are an excellent foundation. One topic of concern is electrical classification of areas. Methanol is a Class 1 Group D material. In addition to explosion-proof equipment, instruments and lighting, I wonder if the dimensions for sumps are adequate. Visualize what would happen to vapor in a serious overflow. Static sparks and lightning are often a surprise. Grounding of all equipment and piping is vital, requiring special care in daily grounding to trucks and rail cars. Discharge from air hoses and even steam can create static discharges. Written hot work permit forms and procedures that require sign-off by both operations supervision and technical personnel are vital.
During the phase of process selection and design, there are opportunities to reduce events and inventory, especially inside buildings, and to reduce the dangers inherent in transfers. A continuous process will normally have less inventory and reduce transfer errors (e.g., overfill, transfer to a wrong tank, pump against closed valves, etc.). Product can be more uniform and reduce rework of off-spec material. This safety feature has led me to develop a very small continuous reactor and an accurate, pulse-free methanol feed pump. Less inventory and risk mean less fire-extinguishing equipment, less insurance premiums and lower operating expenses.
Equipment selection can also reduce fire risk. Vapor pressure of methanol is high (280 psig at 100 psi steam temperature) and can cause overpressure. It is probably best not to heat pure methanol. Heating methanol between closed valves (a blocked-in pump) without a relief valve can rupture pressure gauges. I have witnessed an instrument technician use “autotune mode” in a temperature controller during start-up; it overshot and filled one end of the building with methanol vapors. Fortunately, it did not explode. It is also good practice to minimize connections, flanges and valves to help reduce leaks and errors.
Choices made in construction materials can cause—or help prevent—future fires. The Methanol Institute has a section on corrosion of metals and suitability of gaskets. It is not complete, however, and does not cover corrosion of mixtures of methanol and catalysts (sodium hydroxide, sodium methoxide or sulfuric acid), nor are there charts of corrosion rate as mils/year versus concentration and temperature. Charts for methanol, glycerin, sodium hydroxide and sodium salts can be found in Perry’s Chemical Engineers’ Handbook.
Biodiesel production has no more or less fire hazard than an oil refinery. Plant personnel at all levels need to be vigilant and totally informed, realizing that what they do not know can lead to disaster.
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