There is a major difference between top charging and stamp charging regarding the control of pollution and protection of the environment. That’s because of the difference in the treatment and elimination of the charging gases, while the treatment of pushing emissions is more or less identical.
Concerning the elimination of charging emissions, already by the end of the 1950s, the aim was to implement a charging gas suction system in stamp charging in Germany.
The first devices developed to suck off the charging gases were simple injectors. The injector pipe was extended towards the top by a kind of flair. To create suction compressed air, air blast or steam were used as injector media.
By means of this injectors the charging gases were sucked out of the chamber and then burned after being mixed partially with air.
In the subsequent years, this development was continued and further optimised by using very diverse charging gas elimination systems.
However, the results were not altogether satisfactory, since these systems were either too inefficient or had such a negative impact on oven performance that they could not be used permanently.
The experience gained in the 1960s and beginning of the 1970s resulted in a charging gas cleaning car for sucking off and burning the charging gases.
The charging gases passed through a pipe which could be lowered onto a suction hole on the oven top and were led to the car’s burning chamber lined with fire clay.
There, they were burnt together with the intake air. Passing through several washing stations, the flue gases were freed from solid particles and released to the atmosphere via a ventilator and a chimney.
This technology was put into service in 1974 and was used at Fürstenhausen Coking Plant until 1994.
At the beginning of the 1990s, a charging gas transfer system was developed at Fürstenhausen Coke Plant, Germany especially to work in stamp charging.
In this technology, a U-shaped tube system which can travel along the oven top and can be lowered into mini stand pipes connects the oven to be charged with a neighbouring oven chamber whose coal charge is almost ready for being pushed.
The charging gases are sucked off the oven simultaneously in two different ways.
The first way is the direct sucking off of the charging gases into the collecting main by creating an under-pressure in the oven to be charged by means of a High Pressure Liquid Aspiration (HPLA) system.
By means of the transfer car the remaining part of the charging gases predominantly escaping nearby the open oven door are sucked into the gas collecting main via a neighbouring oven chamber without any emissions.
From there, the charging gases pass on to the existing gas treatment plant together with the coke oven gas.
The charging gas transfer system is completed by a movable sealing frame, which is installed at the charging machine. By means of flexible sealing elements a sufficient sealing is ensured between the coal cake and the oven door during charging.
This measure allows to prevent the charging gases from escaping from the gap between the door frame and the coal cake during charging.
In view of the created suction in the oven the gases are transferred to the crude gas flow.
Moreover, this system helps to prevent larger amounts of air intake into the gas-collecting main sweeping along with coal particles.
This car is basically the “carrier” and manipulator of the tube and suction hole covers. The u- tube is required to transfer a part of the gases developing during charging via the neighbour ovens ascension pipe to the GC Main.
The weight of such a car is by far lower than the weight of a charging car which operates on top of top charged batteries.
To sum up it can be stated that now, the charging gas transfer system and its peripheral installations represent an effective and cheap technology of transferring the whole of the collected charging gases in a closed system to the crude gas of the coke ovens without gas or dust emissions.
By means of this technology, even stricter environmental regulations can be fulfilled without the need of making high investments.
The above picture gives the elements / units in operation during charging and charging gas transfer. The picture shows in principle the function of the Charging Gas Transfer System.
While the cake is being charged, suction is applied to the oven being charged and its second neighbour oven. A part of the charging gas are flowing in the oven being charged directly to the GC main and the other part via the u-tube and the neighbour oven. (Please follow the yellow arrows.)