Patent SG-176997-A1 (SG)
Title: Continuous treatment of water containing carbon black
Inventor: JASS KARL-HEINZ
Filed: 2010-07-14
Abstract: 1 Continuous treatment of soot water[0001] The invention relates to a process for the continuous treatment of soot water thatarises from the partial oxidation of heavy-metal-containing liquid hydrocarbons. 5 [0002] A high-temperature process such as the partial oxidation of heavy-metal-containingliquid hydrocarbons generates dispersed soot that is predominantly discharged from theprocess by scrubbing the soot-containing raw gas with water. The soot water contains up to approximately 2% soot and this soot contains heavy metals, mainly nickel and vanadium.[0003] After scrubbing, the soot water has a temperature of between 150°C and 300°C 10 and a pressure of 40 to 85 bar. Generally, it is passed through a pressure-reducing device and a cooler in order to obtain soot water in an atmospheric state with an acceptable temperature so that it can be further treated. Although the soot water contains a high percentage of water, it hasa highly viscous consistency and the soot hardly precipitates. Dewatering of the soot water is thus highly complex. In practice, the soot water is usually collected in tanks and later subjected 15 to filtration. This is a batch process, the water separated off via the filtration being heated asprocess water and recycled to the process, with the remaining residues being deposited in tanks for further processing.[0004] DE 40 03 242 Al describes a process for separating soot from soot water in whichthe soot water is mixed with sludge at a sludge treatment plant, with a dewatering agent, such 20 as organic flocculant, being added before the soot water undergoes filtration. This process requires large amounts of dewatering agents and a lot of space, which is a major economic burden.[0005] DD 10 63 35 also describes a process for the treatment of soot water, in which alime-containing suspension is added to cause sedimentation. In so doing, the soot water is 25 subjected to a chemical process, meaning that the contaminated effluent cannot be recycled without further treatment.[0006] Publication DE 4331322 Al focuses on a process for separating unwantedmaterials from sludge at a sludge purification plant with settling basins and agitators. In the example application mention is made of the removal of soot and heavy metals downstream of a 30 flue gas desulphurisation unit using a hydrocyclone for thickening. Due to the viscous, pasty quality of soot water arising from the partial oxidation of liquid hydrocarbons, hydrocyclones are unsuitable for use in the dewatering process.[0007] The soot water can also be filtered off in batches. For this, large-volume stackabletanks are required upstream and downstream of the filtration unit; this, however, leads to higher 35 costs than the continuous process. 2[0008] Therefore, the invention is aimed at the problem of developing a process for thecontinuous treatment of soot water from the partial oxidation of heavy-metal-containing liquid hydrocarbons that is technically simpler and more economical from a cost point of view than the state of the art. 5 [0009] The invention achieves the objective via the following process for the continuoustreatment of soot water that accumulates during the partial oxidation of heavy-metal-containing liquid hydrocarbons. In this process the soot water is drawn off from the gasification process at a temperature of 150°C to 300°C and a pressure of 40 to 85 bar, and passes through apressure-reducing device to reduce the pressure to down to approximately 5 bar before it is 10 centrifuged to a solids content of up to 10% at a pressure of up to 5 bar and a temperature of up to 150°C in a pre-dewatering step with no agents being added, a pasty soot sludge rich in heavy metals being obtained and a centrate that is low in heavy metals accumulating. This centrate is recycled, at least in part, to the gasification process as process water.[0010] The soot water from the partial oxidation of heavy-metal-containing liquid 15 hydrocarbons has a temperature of 150°C to 300°C and a pressure of 40 to 85 bar. It must first pass through a pressure-reducing device to reduce the pressure of up to approximately 5 bar.The soot water is cooled to 150°C by a cooler if the temperature of the soot water is over150°C. The dewatering of the soot water is carried out in two steps. In a pre-dewatering step the soot water is passed through a centrifuge at a pressure of up to 5 bar and a temperature of up 20 to 150°C without adding any agents, a viscous soot sludge rich in heavy metals and a centrate low in heavy metals being obtained. The soot sludge contains up to 10% solids. The centrate, which has not been contaminated with any additives, is for the most part recycled to thegasification process as process water. Before the process water that is to be recycled flows back into the gasification process, it is heated to 150°C if the temperature of the centrate is 25 below 150°C. Due to the low temperature loss of the centrate during operation, the centrate also requires only slight reheating.[0011] Some embodiments of the invention envisage the pre-dewatering being carried outusing a sedimentation centrifuge, the sedimentation centrifuge being either a solid-bowl screw-type centrifuge or a disc centrifuge as these centrifuges can perform the dewatering of the soot 30 water at a pressure of up to 5 bar and a temperature of up to 150°C.[0012] In further embodiments of the invention the soot sludge, which is rich in heavymetals, is post-dewatered to a solids content of up to 20%. This is carried out using either continuously operated dewatering equipment, such as a belt filter press, or batchwise-operated dewatering equipment, such as a chamber filter press. The post-dewatering can also be carried 35 out in a drying unit or a spray dryer. After pre-dewatering, the soot sludge can, of course, also be further dewatered in a multi-hearth furnace and subsequently incinerated. 3[0013] The invention is explained by means of Fiq. 1. The pressure of the soot wateraccumulated by the scrubber (1) is first reduced from 40-85 bar to approximately 5 bar in a pressure-reducing device (2). If the temperature of the soot water is over 150°C, the soot water is cooled to approximately 150°C in an air or water cooler (3). After being cooled, the soot water 5 with a pressure of up to 5 bar and a temperature of up to 150°C is pre-dewatered by a centrifuge (4), a pasty soot sludge rich in heavy metals (6) being obtained and a centrate that is low in heavy metals (5) accumulating. This centrate is recycled to the gasification process (10) as process water, the process water being heated to 150°C if the temperature of the centrate isbelow 150°C. The soot sludge (6) is further dewatered to a solids content of up to 20% in a 10 post-dewatering unit (7). Optionally, the post-dewatering (7) can be carried out using filtering agents. The water that is obtained (8) is forwarded for treatment. The filter cake (9) with a solids content of approximately 20% is compact, landfillable and available for further treatment.[0014] The process in accordance with the invention is characterised in that the pre dewatering can be carried out in a centrifuge in a fully mechanical way at a pressure of up to 15 5 bar and a temperature of up to 150°C with no agents being added, the centrate obtainedbeing heated only slightly and recycled to the gasification process as process water. This dispenses with the costs of additional agents and energy, greatly reduces the amount of water consumed in the process and obviates the need for tanks to collect the soot water, which is a major economic advantage over the state of the art. Pre- and post-dewatering can be carried 20 out using simple dewatering equipment. 4[0015] List of reference numbers and designations1 Scrubber2 Pressure-reducing device3 Cooler4 Centrifuge5 Centrate6 Soot sludge7 Post-dewatering unit8 Water9 Filter cake10 Gasification process 5 ClaimsProcess for the continuous treatment of soot water that arises from the partial oxidation of heavy-metal-containing liquid hydrocarbons, the soot water being drawn off from the gasification process at a temperature of 150°C to 300°C and a pressure of 40 to 85 bar,characterised in thatthe soot water passes through a pressure-reducing device to reduce the pressure to down to approximately 5 bar before it is centrifuged to a solids content of up to 10% at a pressure of up to 5 bar and a temperature of up to 150°C in a pre-dewatering step with no agents being added, a pasty soot sludge rich in heavy metals being obtained and a centrate that is low in heavy metals accumulating, the centrate then being recycled, at least in part, to the gasification process as process water.Process according to claim 1, characterised in that the soot water is cooled to 150°C by a cooler if the temperature of the soot water is above 150°C.Process according to claim 1, characterised in that the process water to be recycled is heated to 150°C if the temperature of the centrate is below 150°C.Process according to one of claims 1 to 3, characterised in that the pre-dewatering is carried out with the aid of a sedimentation centrifuge.Process according to claim 4, characterised in that the sedimentation centrifuge is either a solid-bowl screw-type centrifuge or a disc centrifuge.Process according to one of claims 1 to 5, characterised in that the soot sludge, which is rich in heavy metals, is post-dewatered to a solids content of up to 20%.Process according to claim 6, characterised in that the post-dewatering is carried out using continuously operated dewatering equipment.Process according to claim 7, characterised in that the continuously operated dewatering equipment is a belt filter press.Process according to claim 6, characterised in that the post-dewatering is carried out using batchwise-operated dewatering equipment.Process according to claim 9, characterised in that the batchwise-operated dewatering equipment is a chamber filter press.