How can a loving God send anyone to Hell?

Hell appears 31 times in the Old Testament and, without exception, is translated from the Hebrew word Sheol. The same word is translated as "pit" three different times. Sheol is sometimes translated as "the grave" which would infer that hell and the grave are the same, but this is a mistranslation. The proper word for "grave" is "Gibrah", which means grave,burying place, and sepulchre. Hell in the New Testament is the Greek word "Hades". Sheol and Hades are the same thing. Hell is basically a jail the lost souls go to until they are judged and sent to prison in "The Lake of Fire" or "gehenna". There are other compartments as well (Tartarus, The Abyss, The Bottomless pit) but we will not concern ourselves with these at the moment.

The question arises how can a loving God send someone to such a terrible place? Well for starters man was not initially intended to go to hell, this was a place prepared for Satan and his fallen angels (Mat 25:41). God tells us it is not His will that anyone should perish (2Pe 3:9). If it's not His will than whose will is it? Man is afforded every opportunity to accept the free pardon offered when Jesus shed his blood in remission of our sins. God made salvation so simple and easy that one has to literately step over the bloody crucified body of Christ to get to hell. If eternal separation is what men desires then God does not violate their free will and gives them what they want. A place that is eternally separated from God. But in rejecting God they reject everything that is God. God is love, so hell is absent of love, there is only fear and loneliness and misery. God is light, so hell is in darkness. God is mercy, in hell there is no mercy. You see hell is not terrible because God made it terrible, it's terrible because God is not there.

And what of the Lake of Fire? I like Dr. Hugh Ross explanation that demonstrates God compassion even in hell:

These words may sound strange, but in light of God's character and the character of those sentenced to hell, those who inhabit the lake of fire occupy the best possible realm for them. God expresses His love and compassion for hell's inhabitants by afflicting them with sufficient torment to prevent the place from being as bad as its inhabitants have the capacity to make it.
We can only begin to imagine what evil could be expressed by those from whom the restraining influence of God the Spirit has departed. The unleashing of individuals' full potential for cruelty and all manner of evil could make hell vastly more horrible than God designed it to be. The worst thing about hell might be the company its inhabitants must keep. But God will keep in check the horrors these individuals could inflict on one another by immobilizing them, distracting them sufficiently with some kind of pain or discomfort.
The measure of pain and discomfort necessary to restrain each individual in hell will be different. Revelation speaks of differing levels or degrees of torment for those who are sent to hell, torment that is commensurate with each individual's earthly expressions of sin and rebellion. The measure of wickedness a person practiced on earth is the measure of that individual's potential to make life more miserable than it already must be for others in hell. One interpretation suggests that God calibrates each person's torment to exactly the level necessary for restraint of his or her potential for evil.

He goes on to use this story as an illustration:

A good friend of mine once stumbled into a real-life lesson on the consistency of Gods love and His restraint of evildoers in hell. Through the simple error of misreading a map, he was arrested for selling film on the wrong side of the street in the vicinity of Pasadena's Rose Bowl.
Under normal circumstances he would have been driven to the courthouse, cautioned by a judge, and released. But because so many revelers had been arrested the night before, the court system was jammed. All the Pasadena's jail cells were full, as were those in the neighboring communities. My friend, who had never even been sent to the principals office during his school years, was sent to Los Angeles County Jail not just for a few hours but for a whole day and night.
He was placed in a cell with eight other men. While the Los Angeles police do their best to separate violent felons from the rest of the inmate population, their efforts are limited. My friend glanced around to meet eight pairs of eyes staring at this obvious first-timer, each more fearsome than any he had encountered in his life. Including his travels to foreign lands. Eight men watched, waiting for hint to fall asleep. He spent that day and night awake and praying, his back glued to the cell wall.
No physical harm came to him during those agonizing hours, but he does remember wishing that an officer would come to handcuff and leg cuff the others so that he could get a moment's rest. Those cuffs would have brought some torment, of course, but certainly no more than the torment my friend endured. From his perspective, the loving loving thing the police could have done was to restrain his cell mates with cuffs.

You see the flames of the lake of fire can be seen as an act of mercy, the horrors they could inflict on one another would be far worse. I believe however the the degree of punishment will be appropriate to the individual. Just as Christians receive varying degree's of reward based on their works in this life (2Co 5:10, 1Co 3:14,15), like wise the sinners will see their degree of punishment. A person like Hitler, for example, would receive a more severe punishment than the average Joe who never accepted Christ.  Oftentimes we let emotionalism cloud the realities of hell. We look at it from a human perspective, and not God's perspective. Yes God is love, but He's also a judge.