The invention relates to sewage heat recovery facilities, particularly heat recovery units for heating municipal buildings or industrial objects and providing hot water to multi -apartment houses.

Several sewage heat recovery facilities are known to exist. U.S. patent publication No. 4,341,263 describes a sewage heat exchanger receiving warm wastewater to recover and reintroduce energy from the sewage into a house system. This facility relies on a special heat exchange fluid complicates both the system itself and the amount of maintenance required.

International patent application publication No. WO2001/98714 describes a heat recovery unit built into a drainage siphon. The unit consists of heat exchange piping inside the system, providing the recovery of heat from inflowing warm sewage.

The UK patent application publication No. 2 304 977 describes a water supply system with heat recovery where warm sewage is delivered to a heat exchanger before being drained to the sewer system, thus partially recovering contained heat and supplying the heat back to the system.

The UK patent application No. 2 402 204 discloses a heat exchanger that comprises a tank containing and communicating domestic waste water in heat exchange relationship with a supply of fresh cold water. German patent application publication No. 2806029 discloses similar heat recovering system. International patent application publication No. WO2016/033645 discloses a plate-like evaporator shaped to cause incoming fluid from which a heat is to be extracted to follow an extended, circuitous path.

These systems do not provide for long periods of storing sewage in the system, which would allow recovery of heat as efficiently as possible. This is due to the biological activity of sewage, which creates biofilms and other sedimentation within the system. Therefore, such systems are difficult to maintain and require constant monitoring.

The aim of this invention is to improve the effectiveness of a heat recovery facility and increase the efficiency ratio of heat recovery while improving maintenance. The purpose of the invention is achieved by creating a heat recovery unit that contains the following main elements: a warm sewage settling tank, a solid sewage settling tank, a warm wastewater supply pipe, a sewage discharge pipe, a pressure sewage discharge pipe, a sewage pump, a sewage flush valve, a heat exchange circuit, and a heat pump.

The warm sewage settling tank is one of the main elements of the unit, intended for storing warm sewage for effective recovery of the wastewater heat. The sewage heat recovery unit also includes a solid sewage settling tank positioned in the upper part of the solid sewage settling tank, preferably concentrically, and connected (or in in fluid communication) to said warm sewage settling tank via an overflow channel or T- junction. The solid sewage settling tank is connected to a warm sewage supply pipe, through which warm sewage is supplied to the solid sewage settling tank of the sewage heat recovery unit. The warm sewage enters the warm sewage settling tank via the solid particle settling tank's overflow channel or T-junction into the solid warm sewage settling tank, from which it is subsequently removed to the sewer from the lower part of the settling tank, via a discharge pipe connected to the warm sewage settling tank. The overflow channel or T-junction of the solid particle settling tank is the only element through which warm sewage can enter the warm wastewater settling tank from the solid particle settling tank.

The wastewater heat recovery unit also contains a pressure sewage discharge pipe, which connects the solid particle settling tank to the sewage discharge pipe, so that sewage can be sent from the solid particle settling tank to the sewage discharge pipe and into the sewer. One end of the pressure sewage discharge pipe is connected to a sewage pump and the other end is connected to said sewage discharge pipe. The sewage pump is intended to perform two functions. Firstly, the sewage pump sucks up sewage from the solid particle settling tank and sends it to the sewage discharge pipe via the pressure sewage discharge pipe. Secondly, the sewage pump sucks up sewage from the solid particle settling tank and sends it to the sewage flushing valve in the pressure sewage discharge pipe, via which the sewage is sent to the solid particle settling tank's upper layer of solid particles, breaking it up. The sewage pump is situated in the lower part of the solid particle settling tank, preferably near the base of the solid particle settling tank - as far as possible form the biofilm formation zone. The sewage flushing valve is located in the upper part of the solid particle settling tank, so that, when said sewage flushing valve is opened, a stream of sewage is sent to break up the layer of solid particles that has formed inside the solid particle settling tank. This layer is formed mostly at the level of wastewater inside the solid particle settling tank. Such construction allows for effective breakup of the biofilm that inevitably forms in sewage. This increases the required maintenance interval of the unit and reduces running costs.

The sewage heat recovery unit contains a heat exchange circuit inside the sewage settling tank (around the solid particle settling tank) in order to recover heat from the sewage inside the warm sewage settling tank. The heat exchange circuit is connected to a heat pump for recovery of sewage heat.

In one of the solutions, the heat exchange circuit is arranged closer to the outer surface of the solid sewage settling tank than to the inner surface of the warm wastewater settling tank to increase the heat recovery efficiency also from the wastewater flowing into the solid sewage settling tank. In another solution, the heat exchange circuit is placed directly next to the outer surface of the solid particle settling tank, further improving heat recovery efficiency. The heat exchange circuit is placed around the outer wall of the solid particle settling tank, preferably in a helical configuration.

The solution is clarified in attached Fig. 1, which illustrates the principal scheme of the sewage heat recovery unit.

Fig. 1 illustrates a sewage heat recovery unit consisting of warm sewage settling tank warm sewage settling tank 1 and concentrically installed solid particle settling tank 2. Solid particle settling tank 2 is in fluid communication with warm sewage settling tank 1, via the solid particle settling tank 2 overflow T-junction 22 in the upper part of solid particle settling tank 2. The unit also contains a warm wastewater supply pipe 3, which is connected to solid particle settling tank 2 and through which the sewage heat recovery unit's solid particle settling tank 2 receives incoming warm sewage. The inlet of warm wastewater supply pipe 3 is located in the upper part of solid particle settling tank 2. The unit also contains a sewage supply pipe 4, connected to warm sewage settling tank 1 for drainage of the wastewater it contains. Further, the unit contains pressure sewage discharge pipe 5, connecting solid particle settling tank 2 to sewage supply pipe 4. One end of pressure sewage discharge pipe 5, which is inside solid particle settling tank 2, is connected to sewage pump 6. Sewage pump 6 is placed in the lower part of the solid particle settling tank 2 - at the very base of solid particle settling tank 2. Sewage pump 6 is also connected to pressure sewage discharge pipe 5 so that the wastewater pumped out by the sewage pump 6 can be sent to the aforementioned sewage supply pipe 4.

This sewage heat recovery unit is characterised by an additional element - sewage flush valve 8, which is connected to pressure sewage discharge pipe 5 in the upper part or area of solid particle settling tank 2, above the level of contained wastewater, which results in a discharge stream of wastewater when this sewage flush valve 8 is opened, thereby breaking up the upper layer of solid particles that accumulates in solid particle settling tank 2. This upper layer forms at the level of wastewater inside solid particle settling tank 2. The breakup of this layer, or biofilm, eliminates the need for excessive maintenance, thereby reducing running costs. In addition, the unit contains heat exchange circuit 9, located in sewage settling tank 1, around solid particle settling tank 2, for recovering heat from the wastewater contained in the warm sewage settling tank 1, and heat exchange circuit 9 is connected to heat pump 10. Heat exchange circuit 9 is closer to the external surface of solid particle settling tank 2 than to the internal surface of warm sewage settling tank 1, increasing the effectiveness of recovering heat from wastewater that flows into solid particle settling tank 2. Helical heat exchange circuit 9 is situated near the external surface of solid particle settling tank 2.