FIELD

[0001] This specification relates to presses, for example a machine for pressing solid waste to separate a wet fraction from a dry fraction.

BACKGROUND

[0002] Solid waste includes, for example, municipal solid waste (MSW), source separated organics (SSO) and waste from industrial, commercial and institutional (ICI) sources. The waste can de divided into various fractions. For example, organic waste is the part of the waste that is most easily biodegraded. Organic waste is primarily made up of food waste, but may also include leaf and yard waste or other materials. The organic waste fraction is approximately 40% of ordinary MSW after recyclables are removed. SSO may have an organic waste fraction of 80% or more and ICI wastes can have varying amounts of organic material.

[0003] Historically, organic waste was landfilled with other solid waste. However, the organic fraction of solid waste is the major cause of greenhouse gas emissions, leachate and odors in landfills. There is a general trend to divert organic waste for biological treatment, for example by anaerobic digestion (AD) or composting. Most biological treatment steps require some preprocessing of the waste such as debagging and sorting to remove large items such as bottles and cans. Certain biological treatments, such as some composting methods and high-solids slurry and wet (low solids) anaerobic digestion, also require that the waste be reduced in size and homogenized. The size reduction is typically done in a device that comminutes the waste, such as a hammer mill, shredder or pulper. In some cases, the comminuting device also provides a coarse separation of contaminants (i.e. material that is not readily biodegraded, such as plastic). Alternatively, a separate separation device may be added. With adequate processing, at least some of the non-organic waste may be used, for example as refuse derived fuel (RDF), rather than landfilled.

[0004] Recently, there have been various attempts to use presses to separate solid waste into organic and non-organic fractions. The organic fraction may also be called a wet fraction and the non-organic fraction may also be called a dry fraction. In general, the solid waste is loaded into a chamber having a porous wall. A hydraulic ram compresses the waste, which causes liquids and soft materials (i.e. food waste) to be squeezed through the porous wall. Large pieces of primarily non-organic waste are retained in the chamber. The retained fraction, also called the dry fraction, can also include materials, such as wood, that are organic but would be difficult to digest. The retained waste is rejected through a door of the chamber. In some (but not all) cases the pressure of the ram is enough to break open cell walls in the organic waste that is squeezed through the porous wall.

[0005] US Publication 2013/0316428 describes one process in which an organic fraction is separated from solid waste in a press. The organic fraction, alternatively called the wet fraction, is extruded through a grid having small-bore holes, under a pressure higher than the burst pressure of the cell membranes. The cells are disrupted and a gel or paste of a doughy consistency is produced. The gel can be digested in an anaerobic digester. Some examples of presses are described in European Publication Nos. 1207040 and 1568478, International Publication WO 2010/097177, and Italian patent application ITTO201 11068. Commercially available presses include, for example, the Biosqueeze press sold by

Finsterwalder and the VM 2000, Orex and Biorex presses sold by DB Technologies or Anaergia.

INTRODUCTION TO THE INVENTION

[0006] This specification relates to a fastening system for a press useful, for example, for separating solid waste into wet and dry fractions. The solid waste is loaded into a press chamber with one or more porous walls and compressed by a ram to squeeze the wet fraction out of the chamber. Later, a door of the chamber is opened and the retained waste is pushed out of the chamber. The fastening system is used to connect an actuator to the ram.

[0007] In a fastening system described in more detail below, the head of the ram is not attached to the actuator by a common fixed piston rod fastener such as a flange, ball joint, clevis or universal joint. Instead, the fastening system has a pin extending from the actuator through a clearance hole (a hole larger in diameter than the diameter of the pin) in part of the ram. The actuator pushes against the ram directly, i.e. without transferring force through the fastening system, to squeeze waste in the press. On the return stroke, the actuator pulls on the ram through a pin that bears on an inside surface of the ram.

[0008] In a preferred example, the pin bears on an inside surface of the ram through a pair of plates. The adjacent surfaces or the plates have corresponding non-planar shapes. For example, the adjacent surfaces of the plates may be a (truncated) cone and a corresponding inverted (truncated) cone.

BRIEF DESCRIPTION OF THE FIGURES

[0009] Figure 1 is a reproduction of Figures 1 to 3 from International Publication

Number WO 2010/097177.

[0010] Figure 2 is a schematic cross-section of a fastening system between an actuator and a ram.

DETAILED DESCRIPTION

[0011] Solid waste may be, for example, municipal solid waste (MSW), source- separated organics (SSO), industrial, commercial and or institutional waste (ICI), or a mixture of one or more of these or other wastes. Optionally, the waste may be pre-processed to some extent, for example to open bags, to roughly homogenize the waste or to remove very large pieces of waste, metals, or other recyclables.

[0012] The waste is then further processed in a press. The press compresses the waste in a chamber. An organic fraction of the waste, alternatively called the wet fraction, is squeezed through perforations in at least one wall of the chamber. The perforations may be, for example, 4 to 8 mm diameter circular holes. Retained waste, optionally called a dry fraction or non-organic fraction, is initially retained in the chamber. The retained waste is ejected from the chamber after opening a door of the chamber. Presses that treat municipal solid waste (MSW) preferably operate at high pressures, for example 180 to 220 bar.

Presses that operate at lower pressures, for example in a range of about 50 to 150 bar, may be preferred for SSO and ICI waste having high water content.

[0013] The pressed organic waste is typically a viscous paste or slurry with a 20-35 wt% solids content, for example 20-25% when pressing wet commercial waste and 30-35% when pressing residential MSW. The pressed organic waste typically has a 85-95% volatile solids to total solids ratio. The non-volatile solids include floatables (for example small pieces of plastic foil or paper) and grit. The pressed organic waste can be treated further, for example a wet or dry anaerobic digester, or converted into compost or other biosolids.

[0014] The inventors have observed that solid waste presses suffer from a variety of practical problems. A press operates under very high pressure. To minimize leaks, very little space, for example 1 mm or less, is provided around moving parts. The solid waste contains minor amounts of grit such as sand or broken glass. When grit is entrained in waste pressurized in the press, the waste becomes abrasive and some of it leaks into the gaps around moving parts. Moving parts, and surfaces exposed to moving parts, therefore wear down over time.

[0015] One particular issue involves the connection between an actuator, for example a piston from a hydraulic cylinder, and the ram. As parts of the press wear down, the ram can move out of alignment relative to the actuator. Although the misalignment may be small, the force on the ram is large. As a result, wear is accelerated and the connection between the actuator and the ram can break.

[0016] In a ram described in more detail below, the head of the ram is not attached to the actuator by a common fixed piston rod fastener such as a flange, ball joint, clevis or universal joint. Instead, a fastening system has a pin extending from the actuator through a clearance hole in part of the ram. Preferably, an abutment is attached to the pin inside the ram. The actuator pushes against the ram directly, i.e. without transferring force through the fastening system, to squeeze waste in the press. On the return stroke, the actuator pulls on the ram through the pin.

[0017] For context, Figure 1 shows a press described in International Publication

Number WO 2010/097177, Machine for Processing the Organic Fraction of Urban Solid Waste, which is incorporated by reference. In this device, a ram (pressing member 40) compresses waste in a perforated rectilinear tube 30, which provides a pressing chamber. A door (shutting means 49) moves downwards to close the end of tube 30 while the waste is being compressed. A liquid fraction of the waste is squeezed out though the perforations in tube 30. The door 49 then moves upwards, which allows pressing member 40 to eject the remaining solid fraction out of the tube 30. The pressing member 40 is then pulled back to allow more waste to be loaded into the press. An actuator (piston driving means 42) moves the pressing member 40.

[0018] Figure 2 shows a fastening system 100 between an actuator 42 (such as a piston from a hydraulic cylinder) and a ram 40. The fastening system includes a pin 102. One end of pin 102 is attached to the end of the actuator 42. In the example shown, a hole in the end of the actuator 42 is tapped, the pin 102 is threaded and the pin 102 is screwed into the actuator 42. Alternatively, the pin 102 could be press fit into a hole in the actuator 42 or welded to the actuator 42. Part of the pin 102 extends from the actuator 42 and passes through a clearance hole 106 in the ram 40. The clearance hole 106 is larger in diameter than the pin 102, for example by 2 mm or more. A second end of pin 102 inside of ram 40 is accessible through an opening 104 in the ram 40.

[0019] The second end of pin 102 cannot pass through clearance hole 106. When the actuator 42 moves into the chamber to press waste (to the left in Figure 2), the actuator 42 pushes against the ram 40. When the actuator 42 moves out of the chamber (to the right in Figure 2), the actuator 42 pulls on the pin 102 and the pin 102 pushes against the inner surface 108 of ram 40. The clearance hole 106 provides tolerance for axial misalignment of the ram 40 and actuator 42, i.e. displacement of the ram 40 perpendicular to an axial line 118 through the actuator 42.

[0020] The basic action described above can be achieved by any abutment formed in the second end of the pin 102, or attached to the second end of the pin 102, that can bear against the inside surface 108 of ram 40. However, it is preferable for the pin 102 to bear against the inside surface 108 of the ram through a pair of plates 1 10. The plates 110 press against each other through adjacent surfaces. The adjacent surfaces are preferably not flat. In the example shown, a first plate 110a has a flat surface that bears against inside surface 108 and a truncated conical surface that bears against the second plate 110b. The second plate 1 10b has a corresponding inverted truncated conical surface that bears against the conical surface of first plate 110a. The second plate 1 10b also has a flat surface that bears against a nut 1 12 threaded on the second end of pin 102. In the example shown, the nut 1 12 bears on the second plate 1 10b indirectly through an extension ring 1 14 and cover 1 16.

[0021] The cover 1 16, though optional, helps hold the second plate 1 10b in a fixed position relative to the pin 102. The first plate 1 10a is relatively mobile in that it can slide across the inside surface 108 of ram 40. Over repeated cycles of advancing and retracting the ram 40, axial misalignment of the ram 40 and actuator 42 is compensated for by the fastening system 100. While the ram 40 is retracted, the second plate 1 10b may slide laterally over the first plate 100a. When the ram 40 is advanced, the first plate 1 10a may slide back to being concentric with the second plate 1 10b.

[0022] If the chamber that the ram 40 operates in becomes worn, the ram 40 may be displaced from the axial centerline 1 18 through the actuator 42. The fastening system 100 adapts to the misalignment, which avoids transferring forces perpendicular to the axial centerline 1 18 to the actuator 42. This helps prevent damage to the actuator 42, parts that hold the actuator 42 and the fastening system 100. Do to the large pressures possible in a press, even 1 mm of axial misalignment could otherwise damage these parts.