Process hazards High Flow

Examine all process parameters. Parameters (e.g., pressure, temperature, flow rate, level, pH) that are controlled or measured in a process are good indicators of possible process hazards. Process parameters should be examined for all modes of operation, independent of process chemicals, because some hazards exist that do not involve the chemicals. For example, if a process uses high-pressure steam, then both thermal energy and pressure-volume energy hazards exist even though steam is non-toxic, non-flammable, and non-reactive with most materials. 

The fuel gas to a fired heater is controlled by a BPCS control function (function TIC-1), which throttles a fuel control valve, CV-1, as shown in Figure F-3. A hazard analysis was performed to identify process hazards and to determine whether the safeguards were sufficient to mitigate the process hazards. The team determined that when the heater was firing hard, a low-pass flow through the tubes could result in a high firebox temperature with the potential for tube rupture, furnace fire and structural damage to the furnace. 

As with High Flow, the phenomenon of Low Flow is not usually inherently hazardous. However, it can create secondary effects. For example, a low flow of cooling water in a heat exchanger can lead to High Temperature of the process stream. No Flow is usually more serious than Low Flow because its occurrence implies a sudden cessation of a processing activity. Probably, the biggest hazard associated with No How is the possibility of it being followed by Reverse Flow because the upstream and downstream pressures have equalized or even reversed. 

Reverse Flow can create high-consequence hazards because it can lead to the mixing of incompatible chemicals or to the introduction of corrosive chemicals into equipment not designed for them. The cause of Reverse Flow is usually a pressure reversal — a high-pressure section of the process loses pressure process fluids then flow into that section back from low-pressure sections of the process. (The occurrence of reverse flow almost invariably imphes that a check valve and/ or safety instrumented system has failed to prevent the event)... 

In selec ting the machines of choice, the use of specific speed and diameter best describe the flow. Figure 10-67 shows the characteristics of the three types of compressors. Other considerations in chemical plant service such as problems with gases which may be corrosive or have abrasive solids in suspension must be dealt with. Gases at elevated temperatures may create a potential explosion hazard, while air at the same temperatures may be handled qmte normally minute amounts of lubricating oil or water may contaminate the process gas and so may not be permissible, and for continuous-process use, a high degree of equipment rehability is required, since frequent shutdowns for inspec tion or maintenance cannot be tolerated. 

Use of rotary kilns for hazardous waste incineration is becoming more common for disposal of chlorinated hydrocarbons such as polychlorinated biphenyls (PCBs). Flow in these kilns is cocurrent. Major advantages include high temperature, long residence time, and flexibility to process gas, liquid, solid, or drummed wastes. 

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