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IMPROVEMENTS TO GRINDING MILLS ABSTRACT The disclosure relates to a stirred vertical grinding mill comprising a mill body and drive mechanism for rotating a drive shaft of the mill body about 5 a longitudinal axis, wherein the mill body and the drive mechanism are mounted on a frame structure comprising a base frame and a drive frame, respectively, wherein the mill body comprises a mounting assembly for fitting the mill body to the base frame and operatively aligning the mill body to the drive mechanism, wherein the base frame comprises a horizontally arranged 10 rail system configured for engagement with the mounting assembly of the mill body for horizontal movement of the mill body or mill body parts, and wherein the rail system is arranged in a vertical mid region of base frame to horizontally move and vertically support the mill body or mill body part during mounting and dismounting. Also disclosed are a mill liner, a mill shell, and a 15 stirring assembly. (Figure 1A) 1 IMPROVEMENTS TO GRINDING MILLS Technical field The present disclosure relates to grinding mills. 5 Background This disclosure describes a number of design updates for grinding mills of the stirred mill type. A stirred mill, also known as attritor mill, is a type of mill used for grinding and mixing materials such as chemicals, ores, 10 pyrotechnics, paints, and ceramics. It consists of a vertical vessel with a central shaft and impellers that stir the media in a specific pattern. Stirred bead grinding mills are typically used in mineral processing to grind mineral ore particles into smaller sized particles to facilitate further downstream processing, such as separation of the valuable mineral particles 15 from unwanted gangue. For example, mineral ore particles in the range of about 30µm to 4000µm in diameter may be ground down to particles of 5 to 100 µm in diameter. This process is commonly known as fine and ultra-fine grinding. A stirred bead grinding mill typically has a stationary mill body or shell 20 and an internal drive shaft. The shell and the drive shaft can be arranged vertically in the mill; this kind of mill is also known as a tower mill. The drive shaft has a plurality of stirring elements, such as rotor disks or rotors, so that rotation of the drive shaft also rotates the stirring elements, which in turn stirs a suitable grinding media, and the mineral ore particles, in the form of a feed 25 slurry, passes through this stirred bed of media. The resulting stirring action causes the mineral ore particles to be ground into smaller sized particles. In other words, in contrast to tumbling mills such as ball mills where motion is imparted to the charge via the rotation of the mill shell, in tower and stirred mills motion is imparted to the charge by the movement of an internal stirrer 30 while the shell remains stationary. Exemplary stirred bead grinding mills are known from WO 2017/017315 A1 and WO 2018/138405 A1. 2 One challenge with vertically arranged stirred grinding mills is the ever growing demand of capacity and with that a growing demand on larger and larger vertically arranged stirred grinding mills. Thus, there is a need for facilitating larger and larger stirred grinding mills, i.e. upsizing the vertical 5 stirred grinding mills, but still maintaining targeted grinding sizes, stability and robustness of the vertical stirred grinding mills as well as safeguarding the working environment for staff handling the operation and maintenance of the vertical stirred grinding mills. Another challenge with stirred grinding mills is the mill shell liners 10 arranged on the inner circumferential surface grinding chamber to protect the inner peripheral surface from wear. In spite of many improvement over the years there is still need for reducing the time and work required for replacement of the components, reducing downtime, and/or reducing maintenance costs. 15 Summary of invention According to a first aspect of the present disclosure, it is an object to provide a stirred vertical grinding mill that provides for upsizing with maintained performance, stability and robustness, as well as safeguarding the 20 working environment for the staff handling the operation and maintenance of stirred vertical grinding mills. This object is achieved by means of a stirred vertical grinding mill according to below disclosed embodiments of the first aspect (1st aspect EB): 1st aspect EB 1: A stirred vertical grinding mill comprising a mill 25 body and drive mechanism for rotating a drive shaft of the mill body about a longitudinal axis, wherein the mill body and the drive mechanism are mounted on a frame structure comprising a base frame and a drive frame, respectively, wherein the mill body comprises a mounting assembly for fitting the mill body to the base frame and operatively aligning the mill body to the drive 30 mechanism, wherein the base frame comprises a horizontally arranged rail system configured for engagement with the mounting assembly of the mill body for horizontal movement of the mill body or mill body parts, and wherein 3 the rail system is arranged in a vertical mid region of base frame to horizontally move and vertically support the mill body or mill body part during mounting and dismounting. The vertical mid region may be positioned at or close to the a 5 geometrical centre of the mill body. It is however conceivable that the vertical mid region is positioned somewhat higher, or somewhat lower, than the geometrical centre, for example within +/- 20% of the geometrical centre. 1st aspect EB 2: A stirred vertical grinding mill according to 1st aspect EB 1, wherein the base frame comprises at least two base frame parts 10 arranged with a horizontal distance to each other and connected by at least one bridging head frame providing a bridge opening, wherein the horizontally arranged rail system bridges the bridge opening. 1st aspect EB 3. A stirred vertical grinding mill according to 1st aspect EB 1 or 1st aspect EB 2, wherein stirred vertical grinding mill further 15 comprises a stirring assembly for arrangement in a grinding chamber of the mill body and rotating therein, wherein the base frame comprises a bridge crane arranged for vertically lifting/lowering and horizontally moving the stirring assembly, and wherein the bridge crane is at least arranged to movement over and along the bridge opening. 20 1st aspect EB4. A stirred vertical grinding mill according to 1st aspect EB 3, wherein the base frame further comprises a stirring assembly rack detachably arranged in an end of the bridge opening in one of the at least two base frame parts, which detachable stirring assembly rack is configured for fastening and unfastening the stirring assembly thereto, and 25 which detachable stirring assembly rack may be detached from the base frame part and lowered down for separate maintenance or exchange of the stirring assembly, and then hosting up again for mounting the stirring assembly within the grinding chamber of the mill body. 1st aspect EB 5. A stirred vertical grinding mill arrangement, 30 comprising multiple stirred vertical grinding mills according to any one of 1st aspect EB2 to 1st aspect EB4, wherein the bridge openings are arranged aligned and wherein the at least two base frame parts, for each stirred vertical 4 grinding mill arranged on respective side of the bridge opening, are interconnected on each respective side of the bridge opening. 1st aspect EB 6. A stirred vertical grinding mill arrangement 5 according to 1st aspect EB 5, wherein the stirred vertical grinding mill arrangement comprises at least one common bridge crane arranged for vertically lifting/lowering and horizontally moving the stirring assemblies of the stirred vertical grinding mill arrangement. 1st aspect EB 7. A stirred vertical grinding mill arrangement 10 according to 1st aspect EB 5 or 1st aspect EB 6, wherein the stirred vertical grinding mill arrangement comprises at least one common stirring assembly rack detachable arranged and aligned with the bridge opening in one of the at least two base frame parts. According to a second aspect of the present disclosure, it is an object 15 to provide mill shell liners reducing the time and work required for replacement of the components, reducing downtime, and/or reducing maintenance costs. This object is achieved by means of a mill liner according to below disclosed embodiments of the second aspect (2nd aspect EB): 20 2nd aspect EB 1: A mill liner for a stirred grinding mill, wherein the mill liner is configured to be releasably fitted to the inside of the shell of the mill within a grinding chamber thereof, wherein the mill liner is curved into the shape of segment of a hollow cylinder, and wherein each mill liner comprises a stator ring segment and a wall liner segment provid...