October 2014 - Cement Plants - Tyre Feed Valves
October 2014 - Cement Plants - Tyre Feed Valves
Complete Valve Solution
Complete Valve Solution
by Wayne Akers
European Gate Valves Ltd, UK.
By their very nature, tyre feed systems are exposed to very high temperatures and the abrasiveness of tyre chips (see Figure 1). An essential part of these systems are valves to regulate the flow of the feedstock from the hoppers to the kiln. Like the entire feed system they must be able to withstand the harsh operating conditions.
To meet this requirement, European Gate Valves has developed a full feed-side valve package, consisting of a water gate, double-flap valve and fire gate (see Figure 2). The valves, which are modular in design, can be installed individually or as a three-valve stack.
The valves can withstand temperatures of up to 1000°C and abrasive operating conditions. Moreover, they are designed with ease of maintenance in mind and minimum service times to replace parts as required
The Water Gate
The water gate is a water-tight isolation valve that offers kiln feed-side protection against firefighting suppression systems. Manufactured entirely in stainless steel, this valve has high-temperature seals to hold back water and foam if the feedstock catches fire. A separate or integral failsafe system slams the gate shut upon loss of air or power.
Valves form a key part in regulating the feed volumes of alternative fuels such as tyres into the kiln. However, their operating environment is harsh and their design must therefore reflect this to ensure a long valve life and low maintenance.
Figure 1. tyre chip feeder installation
High-temperature double-flap valve
This double-flap valve has a body of fully-cast stainless steel with stainless steel seats and flaps which can handle temperatures up to 1000°C
This type of valve offers several benefits. The CH Tall Series double-flap valve has a fully-open throat when the tyre chips drop down through the valve. This avoids interlocking tyre chips and bird's nest formation as is the case above a rotary feeder. The valve has no wiping action to wear the valve or trap tyre chips between the body housing and blade
In addition, it also serves as an air lock into the cement kiln. The two halves that constitute a double-flap valve are sequenced so that only one flap is opened at a time, therefore giving an airlock to the kiln and also a metered amount of tyre chips into the kiln at one time. The space between the two halves of a double-flap valve is the maximum amount of air that can be drawn into a kiln when the tyre chips are dropped in. This will never change over the life of the valve and can be easily calculated.
Figure 2. a full feed-side valve package, suitable to operate in the high-temperature, abrasive environment of the cement plant
A rotary feeder by comparison requires tolerances between the blade tip and housing for it to operate. The tolerances allow air to pass from one environment to another, even when the rotary feeder is not operating. Once the rotary feeder is operating the leakage rate soars because not only are the pockets on the feeder pulling in air, but air is freely passing the radial and axial clearances. Air leakage into kilns increase fuel consumption and CO2 footprint.
Actuation
Double-flap valves can be actuated a number of ways, but when it comes to kiln-side feed duty, several potential issues must be considered. If plant pneumatics were to fail, then normally the flaps on a double-flap valve would both drop open. This would allow an uncontrolled feed as well as uncontrolled air into the kiln, negatively impacting the production process. With linear pneumatic actuation a failsafe could be supplied to push the flap closed if a plant failure were detected, be that plant air or electric. With rotary pneumatic actuation a spring return could be used to close both gates.
Feeding into precalciners and preheaters
Whole tyres can be introduced into the preheater/precalciner kilns using double-flap valves. The valve is mounted in the mid-section of a straight kiln's feeding system. Introducing the tyres at this point carries the greatest potential for combustion of whole used tyres
Fire gate
At the kiln side, the fire gate is manufactured entirely in stainless steel and is designed to handle up to 1000°C for a sustained period without damage. The cast stainless isolation gate will expand when achieving its maximum soak temperatures, but unlike its rolled stainless steel counterpart, it will not warp and jam the valve.
An integral failsafe system is typically included which shuts the valve in cases of air or power failure.
Case study: UK cement plant
European Gate Valves, most recent installation was at a UK-based cement plant in south Wales in May 2014.
At the works, the current high-temperature isolation gate on the kiln feed line was jamming every time it operated.
Solving this issue on a large gate under extreme temperatures brings its own set of problems. Moreover, the gate did not have a mechanism to automatically shut when plant pneumatics or power failed. Should
the kiln pressurise, this presented huge risk to the feedstock. European Gate Valves installed a new
fire gate, designed and custom-made to customer's requirements.
The fire gate was manufactured with sufficient tolerance to expand during its temperature absorption and not jam
during operation at 1000°C. This part was cast rather than standard rolled plate and is key in the successful operation of such a gate. Standard rolled plate will
bend and warp under such high absorbed
temperatures and jam during operation.
Figure 3: the fire gate installed with double actuator
In addition, European Gate Valves supplied a pneumatic failsafe with the fire gate to slam shut the isolation gate upon losing plant pneumatics or electrical power. This mechanism consists of an air reservoir and pneumatics panel. The pneumatics panel can be for a single gate or up to
four gates. Depending upon the size and type of actuation, the air reservoir and panel can be mounted on the gate itself or supplied separately to be wall mounted
